[PATCH] tun: avoid double free in tun_free_netdev

Avoid double free in tun_free_netdev() by clearing tun->security
after free and using it to indicate that free has already been done.

BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605

CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
 print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
 kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
 ____kasan_slab_free mm/kasan/common.c:346 [inline]
 __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:1723 [inline]
 slab_free_freelist_hook mm/slub.c:1749 [inline]
 slab_free mm/slub.c:3513 [inline]
 kfree+0xac/0x2d0 mm/slub.c:4561
 selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
 security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
 tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
 netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
 rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
 __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
 tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported-by: syzkaller <redacted>
Signed-off-by: George Kennedy <redacted>
---
 drivers/net/tun.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1572878..617c71f 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c

@@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
 	dev->tstats = NULL;
 
 	tun_flow_uninit(tun);
-	security_tun_dev_free_security(tun->security);
+	if (tun->security) {
+		security_tun_dev_free_security(tun->security);
+		tun->security = NULL;
+	}
 	__tun_set_ebpf(tun, &tun->steering_prog, NULL);
 	__tun_set_ebpf(tun, &tun->filter_prog, NULL);
 }

@@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 
 err_free_flow:
 	tun_flow_uninit(tun);
-	security_tun_dev_free_security(tun->security);
+	if (tun->security) {
+		security_tun_dev_free_security(tun->security);
+		/* Let tun_free_netdev() know the free has already been done. */
+		tun->security = NULL;
+	}
 err_free_stat:
 	free_percpu(dev->tstats);
 err_free_dev:

-- 
1.8.3.1

On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote:

What protects this from racing with tun_free_netdev()?

And why can't security_tun_dev_free_security() handle a NULL value?

thanks,

greg k-h

On 12/8/2021 10:40 AM, Greg KH wrote:

On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote:

quoted

Avoid double free in tun_free_netdev() by clearing tun->security
after free and using it to indicate that free has already been done.

BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605

CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS
Call Trace:
  <TASK>
  __dump_stack lib/dump_stack.c:88 [inline]
  dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
  print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
  kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
  ____kasan_slab_free mm/kasan/common.c:346 [inline]
  __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
  kasan_slab_free include/linux/kasan.h:235 [inline]
  slab_free_hook mm/slub.c:1723 [inline]
  slab_free_freelist_hook mm/slub.c:1749 [inline]
  slab_free mm/slub.c:3513 [inline]
  kfree+0xac/0x2d0 mm/slub.c:4561
  selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
  security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
  tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
  netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
  rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
  __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
  tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
  vfs_ioctl fs/ioctl.c:51 [inline]
  __do_sys_ioctl fs/ioctl.c:874 [inline]
  __se_sys_ioctl fs/ioctl.c:860 [inline]
  __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported-by: syzkaller <redacted>
Signed-off-by: George Kennedy <redacted>
---
  drivers/net/tun.c | 11 +++++++++--
  1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1572878..617c71f 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c

@@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
  	dev->tstats = NULL;
  
  	tun_flow_uninit(tun);
-	security_tun_dev_free_security(tun->security);
+	if (tun->security) {
+		security_tun_dev_free_security(tun->security);
+		tun->security = NULL;
+	}
  	__tun_set_ebpf(tun, &tun->steering_prog, NULL);
  	__tun_set_ebpf(tun, &tun->filter_prog, NULL);
  }

@@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
  
  err_free_flow:
  	tun_flow_uninit(tun);
-	security_tun_dev_free_security(tun->security);
+	if (tun->security) {
+		security_tun_dev_free_security(tun->security);
+		/* Let tun_free_netdev() know the free has already been done. */
+		tun->security = NULL;

What protects this from racing with tun_free_netdev()?

tun_free_netdev() is called after err_free_flow has already done the free. rtnl_lock() and rtnl_unlock() prevent the race.

Here is the full KASAN report:

Syzkaller hit 'KASAN: invalid-free in selinux_tun_dev_free_security' bug.

==================================================================
BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605

CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7860+a7792d29 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
 print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
 kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
 ____kasan_slab_free mm/kasan/common.c:346 [inline]
 __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:1723 [inline]
 slab_free_freelist_hook mm/slub.c:1749 [inline]
 slab_free mm/slub.c:3513 [inline]
 kfree+0xac/0x2d0 mm/slub.c:4561
 selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
 security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
 tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
 netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
 rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
 __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
 tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fd496f4c289
Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d b7 db 2c 00 f7 d8 64 89 01 48
RSP: 002b:00007fd497632e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000603190 RCX: 00007fd496f4c289
RDX: 0000000020000240 RSI: 00000000400454ca RDI: 0000000000000003
RBP: 0000000000603198 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000060319c
R13: 0000000000021000 R14: 0000000000000000 R15: 00007fd497633700
 </TASK>

Allocated by task 25750:
 kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc+0x8d/0xb0 mm/kasan/common.c:522
 kasan_kmalloc include/linux/kasan.h:269 [inline]
 kmem_cache_alloc_trace+0x18a/0x2d0 mm/slub.c:3261
 kmalloc include/linux/slab.h:590 [inline]
 kzalloc include/linux/slab.h:724 [inline]
 selinux_tun_dev_alloc_security+0x50/0x180 security/selinux/hooks.c:5594
 security_tun_dev_alloc_security+0x51/0xb0 security/security.c:2336
 tun_set_iff.constprop.66+0x107f/0x1d10 drivers/net/tun.c:2727
 __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
 tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Freed by task 25750:
 kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
 kasan_set_track+0x25/0x30 mm/kasan/common.c:46
 kasan_set_free_info+0x24/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free mm/kasan/common.c:366 [inline]
 ____kasan_slab_free mm/kasan/common.c:328 [inline]
 __kasan_slab_free+0xe8/0x120 mm/kasan/common.c:374
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:1723 [inline]
 slab_free_freelist_hook mm/slub.c:1749 [inline]
 slab_free mm/slub.c:3513 [inline]
 kfree+0xac/0x2d0 mm/slub.c:4561
 selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
 security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
 tun_set_iff.constprop.66+0x9f9/0x1d10 drivers/net/tun.c:2782
 __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
 tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff888066b87370
 which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes inside of
 8-byte region [ffff888066b87370, ffff888066b87378)
The buggy address belongs to the page:
page:0000000003b0639d refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x66b87
flags: 0xfffffc0000200(slab|node=0|zone=1|lastcpupid=0x1fffff)
raw: 000fffffc0000200 dead000000000100 dead000000000122 ffff888100042280
raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888066b87200: fc fb fc fc fc fc 00 fc fc fc fc fa fc fc fc fc
 ffff888066b87280: fa fc fc fc fc fa fc fc fc fc fb fc fc fc fc fa

ffff888066b87300: fc fc fc fc 00 fc fc fc fc fb fc fc fc fc fa fc

                                                             ^
 ffff888066b87380: fc fc fc fa fc fc fc fc 00 fc fc fc fc fa fc fc
 ffff888066b87400: fc fc fa fc fc fc fc fa fc fc fc fc fa fc fc fc
==================================================================

And why can't security_tun_dev_free_security() handle a NULL value?

security_tun_dev_free_security() could be modified to handle the NULL value.

George

thanks,

greg k-h

On Wed, Dec 08, 2021 at 11:29:47AM -0500, George Kennedy wrote:

On 12/8/2021 10:40 AM, Greg KH wrote:

quoted

On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote:

quoted

Avoid double free in tun_free_netdev() by clearing tun->security
after free and using it to indicate that free has already been done.

BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605

CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS
Call Trace:
  <TASK>
  __dump_stack lib/dump_stack.c:88 [inline]
  dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
  print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
  kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
  ____kasan_slab_free mm/kasan/common.c:346 [inline]
  __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
  kasan_slab_free include/linux/kasan.h:235 [inline]
  slab_free_hook mm/slub.c:1723 [inline]
  slab_free_freelist_hook mm/slub.c:1749 [inline]
  slab_free mm/slub.c:3513 [inline]
  kfree+0xac/0x2d0 mm/slub.c:4561
  selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
  security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
  tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
  netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
  rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
  __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
  tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
  vfs_ioctl fs/ioctl.c:51 [inline]
  __do_sys_ioctl fs/ioctl.c:874 [inline]
  __se_sys_ioctl fs/ioctl.c:860 [inline]
  __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported-by: syzkaller <redacted>
Signed-off-by: George Kennedy <redacted>
---
  drivers/net/tun.c | 11 +++++++++--
  1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1572878..617c71f 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c

@@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
  	dev->tstats = NULL;
  	tun_flow_uninit(tun);
-	security_tun_dev_free_security(tun->security);
+	if (tun->security) {
+		security_tun_dev_free_security(tun->security);
+		tun->security = NULL;
+	}
  	__tun_set_ebpf(tun, &tun->steering_prog, NULL);
  	__tun_set_ebpf(tun, &tun->filter_prog, NULL);
  }

@@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
  err_free_flow:
  	tun_flow_uninit(tun);
-	security_tun_dev_free_security(tun->security);
+	if (tun->security) {
+		security_tun_dev_free_security(tun->security);
+		/* Let tun_free_netdev() know the free has already been done. */
+		tun->security = NULL;

What protects this from racing with tun_free_netdev()?

tun_free_netdev() is called after err_free_flow has already done the free.
rtnl_lock() and rtnl_unlock() prevent the race.

Ok, good, it wasn't obvious from the context here.

Here is the full KASAN report:

Syzkaller hit 'KASAN: invalid-free in selinux_tun_dev_free_security' bug.

==================================================================
BUG: KASAN: double-free or invalid-free in
selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605

CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7860+a7792d29
04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
 print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
 kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
 ____kasan_slab_free mm/kasan/common.c:346 [inline]
 __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:1723 [inline]
 slab_free_freelist_hook mm/slub.c:1749 [inline]
 slab_free mm/slub.c:3513 [inline]
 kfree+0xac/0x2d0 mm/slub.c:4561
 selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
 security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
 tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
 netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
 rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
 __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
 tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fd496f4c289
Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff
73 01 c3 48 8b 0d b7 db 2c 00 f7 d8 64 89 01 48
RSP: 002b:00007fd497632e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000603190 RCX: 00007fd496f4c289
RDX: 0000000020000240 RSI: 00000000400454ca RDI: 0000000000000003
RBP: 0000000000603198 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000060319c
R13: 0000000000021000 R14: 0000000000000000 R15: 00007fd497633700
 </TASK>

Allocated by task 25750:
 kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc+0x8d/0xb0 mm/kasan/common.c:522
 kasan_kmalloc include/linux/kasan.h:269 [inline]
 kmem_cache_alloc_trace+0x18a/0x2d0 mm/slub.c:3261
 kmalloc include/linux/slab.h:590 [inline]
 kzalloc include/linux/slab.h:724 [inline]
 selinux_tun_dev_alloc_security+0x50/0x180 security/selinux/hooks.c:5594
 security_tun_dev_alloc_security+0x51/0xb0 security/security.c:2336
 tun_set_iff.constprop.66+0x107f/0x1d10 drivers/net/tun.c:2727
 __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
 tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Freed by task 25750:
 kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
 kasan_set_track+0x25/0x30 mm/kasan/common.c:46
 kasan_set_free_info+0x24/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free mm/kasan/common.c:366 [inline]
 ____kasan_slab_free mm/kasan/common.c:328 [inline]
 __kasan_slab_free+0xe8/0x120 mm/kasan/common.c:374
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:1723 [inline]
 slab_free_freelist_hook mm/slub.c:1749 [inline]
 slab_free mm/slub.c:3513 [inline]
 kfree+0xac/0x2d0 mm/slub.c:4561
 selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
 security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
 tun_set_iff.constprop.66+0x9f9/0x1d10 drivers/net/tun.c:2782
 __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
 tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff888066b87370
 which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes inside of
 8-byte region [ffff888066b87370, ffff888066b87378)
The buggy address belongs to the page:
page:0000000003b0639d refcount:1 mapcount:0 mapping:0000000000000000
index:0x0 pfn:0x66b87
flags: 0xfffffc0000200(slab|node=0|zone=1|lastcpupid=0x1fffff)
raw: 000fffffc0000200 dead000000000100 dead000000000122 ffff888100042280
raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888066b87200: fc fb fc fc fc fc 00 fc fc fc fc fa fc fc fc fc
 ffff888066b87280: fa fc fc fc fc fa fc fc fc fc fb fc fc fc fc fa

quoted

ffff888066b87300: fc fc fc fc 00 fc fc fc fc fb fc fc fc fc fa fc

                                                             ^
 ffff888066b87380: fc fc fc fa fc fc fc fc 00 fc fc fc fc fa fc fc
 ffff888066b87400: fc fc fa fc fc fc fc fa fc fc fc fc fa fc fc fc
==================================================================

quoted

And why can't security_tun_dev_free_security() handle a NULL value?

security_tun_dev_free_security() could be modified to handle the NULL value.

That's fine, most of this patch would still be needed even if you do
that.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

On Wed, 8 Dec 2021 11:29:47 -0500
George Kennedy [off-list ref] wrote:

On 12/8/2021 10:40 AM, Greg KH wrote:

quoted

On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote:  

quoted

Avoid double free in tun_free_netdev() by clearing tun->security
after free and using it to indicate that free has already been done.

BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605

CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS
Call Trace:
  <TASK>
  __dump_stack lib/dump_stack.c:88 [inline]
  dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
  print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
  kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
  ____kasan_slab_free mm/kasan/common.c:346 [inline]
  __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
  kasan_slab_free include/linux/kasan.h:235 [inline]
  slab_free_hook mm/slub.c:1723 [inline]
  slab_free_freelist_hook mm/slub.c:1749 [inline]
  slab_free mm/slub.c:3513 [inline]
  kfree+0xac/0x2d0 mm/slub.c:4561
  selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
  security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
  tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
  netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
  rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
  __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
  tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
  vfs_ioctl fs/ioctl.c:51 [inline]
  __do_sys_ioctl fs/ioctl.c:874 [inline]
  __se_sys_ioctl fs/ioctl.c:860 [inline]
  __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported-by: syzkaller <redacted>
Signed-off-by: George Kennedy <redacted>
---
  drivers/net/tun.c | 11 +++++++++--
  1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1572878..617c71f 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c

@@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
  	dev->tstats = NULL;
  
  	tun_flow_uninit(tun);
-	security_tun_dev_free_security(tun->security);
+	if (tun->security) {
+		security_tun_dev_free_security(tun->security);
+		tun->security = NULL;
+	}
  	__tun_set_ebpf(tun, &tun->steering_prog, NULL);
  	__tun_set_ebpf(tun, &tun->filter_prog, NULL);
  }

@@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
  
  err_free_flow:
  	tun_flow_uninit(tun);
-	security_tun_dev_free_security(tun->security);
+	if (tun->security) {
+		security_tun_dev_free_security(tun->security);
+		/* Let tun_free_netdev() know the free has already been done. */
+		tun->security = NULL;  

What protects this from racing with tun_free_netdev()?  

tun_free_netdev() is called after err_free_flow has already done the 
free. rtnl_lock() and rtnl_unlock() prevent the race.

Here is the full KASAN report:

Syzkaller hit 'KASAN: invalid-free in selinux_tun_dev_free_security' bug.

==================================================================
BUG: KASAN: double-free or invalid-free in 
selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605

CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7860+a7792d29 
04/01/2014
Call Trace:
  <TASK>
  __dump_stack lib/dump_stack.c:88 [inline]
  dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
  print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
  kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
  ____kasan_slab_free mm/kasan/common.c:346 [inline]
  __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
  kasan_slab_free include/linux/kasan.h:235 [inline]
  slab_free_hook mm/slub.c:1723 [inline]
  slab_free_freelist_hook mm/slub.c:1749 [inline]
  slab_free mm/slub.c:3513 [inline]
  kfree+0xac/0x2d0 mm/slub.c:4561
  selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
  security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
  tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
  netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
  rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
  __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
  tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
  vfs_ioctl fs/ioctl.c:51 [inline]
  __do_sys_ioctl fs/ioctl.c:874 [inline]
  __se_sys_ioctl fs/ioctl.c:860 [inline]
  __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fd496f4c289
Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89 
f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 
f0 ff ff 73 01 c3 48 8b 0d b7 db 2c 00 f7 d8 64 89 01 48
RSP: 002b:00007fd497632e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000603190 RCX: 00007fd496f4c289
RDX: 0000000020000240 RSI: 00000000400454ca RDI: 0000000000000003
RBP: 0000000000603198 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000060319c
R13: 0000000000021000 R14: 0000000000000000 R15: 00007fd497633700
  </TASK>

Allocated by task 25750:
  kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
  kasan_set_track mm/kasan/common.c:46 [inline]
  set_alloc_info mm/kasan/common.c:434 [inline]
  ____kasan_kmalloc mm/kasan/common.c:513 [inline]
  __kasan_kmalloc+0x8d/0xb0 mm/kasan/common.c:522
  kasan_kmalloc include/linux/kasan.h:269 [inline]
  kmem_cache_alloc_trace+0x18a/0x2d0 mm/slub.c:3261
  kmalloc include/linux/slab.h:590 [inline]
  kzalloc include/linux/slab.h:724 [inline]
  selinux_tun_dev_alloc_security+0x50/0x180 security/selinux/hooks.c:5594
  security_tun_dev_alloc_security+0x51/0xb0 security/security.c:2336
  tun_set_iff.constprop.66+0x107f/0x1d10 drivers/net/tun.c:2727
  __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
  tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
  vfs_ioctl fs/ioctl.c:51 [inline]
  __do_sys_ioctl fs/ioctl.c:874 [inline]
  __se_sys_ioctl fs/ioctl.c:860 [inline]
  __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x44/0xae

Freed by task 25750:
  kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
  kasan_set_track+0x25/0x30 mm/kasan/common.c:46
  kasan_set_free_info+0x24/0x40 mm/kasan/generic.c:370
  ____kasan_slab_free mm/kasan/common.c:366 [inline]
  ____kasan_slab_free mm/kasan/common.c:328 [inline]
  __kasan_slab_free+0xe8/0x120 mm/kasan/common.c:374
  kasan_slab_free include/linux/kasan.h:235 [inline]
  slab_free_hook mm/slub.c:1723 [inline]
  slab_free_freelist_hook mm/slub.c:1749 [inline]
  slab_free mm/slub.c:3513 [inline]
  kfree+0xac/0x2d0 mm/slub.c:4561
  selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
  security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
  tun_set_iff.constprop.66+0x9f9/0x1d10 drivers/net/tun.c:2782
  __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
  tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
  vfs_ioctl fs/ioctl.c:51 [inline]
  __do_sys_ioctl fs/ioctl.c:874 [inline]
  __se_sys_ioctl fs/ioctl.c:860 [inline]
  __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff888066b87370
  which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes inside of
  8-byte region [ffff888066b87370, ffff888066b87378)
The buggy address belongs to the page:
page:0000000003b0639d refcount:1 mapcount:0 mapping:0000000000000000 
index:0x0 pfn:0x66b87
flags: 0xfffffc0000200(slab|node=0|zone=1|lastcpupid=0x1fffff)
raw: 000fffffc0000200 dead000000000100 dead000000000122 ffff888100042280
raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff888066b87200: fc fb fc fc fc fc 00 fc fc fc fc fa fc fc fc fc
  ffff888066b87280: fa fc fc fc fc fa fc fc fc fc fb fc fc fc fc fa
 >ffff888066b87300: fc fc fc fc 00 fc fc fc fc fb fc fc fc fc fa fc  
                                                              ^
  ffff888066b87380: fc fc fc fa fc fc fc fc 00 fc fc fc fc fa fc fc
  ffff888066b87400: fc fc fa fc fc fc fc fa fc fc fc fc fa fc fc fc
==================================================================

quoted

And why can't security_tun_dev_free_security() handle a NULL value?  

security_tun_dev_free_security() could be modified to handle the NULL value.

It looks like a lot of the problem is duplicate unwind.
Why does err_free_flow, err_free_stat etc unwinds need to exist if
the free_netdev is going to do same thing.

On 12/8/2021 11:36 AM, Stephen Hemminger wrote:

On Wed, 8 Dec 2021 11:29:47 -0500
George Kennedy [off-list ref] wrote:

quoted

On 12/8/2021 10:40 AM, Greg KH wrote:

quoted

On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote:

quoted

Avoid double free in tun_free_netdev() by clearing tun->security
after free and using it to indicate that free has already been done.

BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605

CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS
Call Trace:
   <TASK>
   __dump_stack lib/dump_stack.c:88 [inline]
   dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
   print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
   kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
   ____kasan_slab_free mm/kasan/common.c:346 [inline]
   __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
   kasan_slab_free include/linux/kasan.h:235 [inline]
   slab_free_hook mm/slub.c:1723 [inline]
   slab_free_freelist_hook mm/slub.c:1749 [inline]
   slab_free mm/slub.c:3513 [inline]
   kfree+0xac/0x2d0 mm/slub.c:4561
   selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
   security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
   tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
   netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
   rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
   __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
   tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
   vfs_ioctl fs/ioctl.c:51 [inline]
   __do_sys_ioctl fs/ioctl.c:874 [inline]
   __se_sys_ioctl fs/ioctl.c:860 [inline]
   __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported-by: syzkaller <redacted>
Signed-off-by: George Kennedy <redacted>
---
   drivers/net/tun.c | 11 +++++++++--
   1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1572878..617c71f 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c

@@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
   	dev->tstats = NULL;
   
   	tun_flow_uninit(tun);
-	security_tun_dev_free_security(tun->security);
+	if (tun->security) {
+		security_tun_dev_free_security(tun->security);
+		tun->security = NULL;
+	}
   	__tun_set_ebpf(tun, &tun->steering_prog, NULL);
   	__tun_set_ebpf(tun, &tun->filter_prog, NULL);
   }

@@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
   
   err_free_flow:
   	tun_flow_uninit(tun);
-	security_tun_dev_free_security(tun->security);
+	if (tun->security) {
+		security_tun_dev_free_security(tun->security);
+		/* Let tun_free_netdev() know the free has already been done. */
+		tun->security = NULL;

What protects this from racing with tun_free_netdev()?

tun_free_netdev() is called after err_free_flow has already done the
free. rtnl_lock() and rtnl_unlock() prevent the race.

Here is the full KASAN report:

Syzkaller hit 'KASAN: invalid-free in selinux_tun_dev_free_security' bug.

==================================================================
BUG: KASAN: double-free or invalid-free in
selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605

CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7860+a7792d29
04/01/2014
Call Trace:
   <TASK>
   __dump_stack lib/dump_stack.c:88 [inline]
   dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
   print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
   kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
   ____kasan_slab_free mm/kasan/common.c:346 [inline]
   __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
   kasan_slab_free include/linux/kasan.h:235 [inline]
   slab_free_hook mm/slub.c:1723 [inline]
   slab_free_freelist_hook mm/slub.c:1749 [inline]
   slab_free mm/slub.c:3513 [inline]
   kfree+0xac/0x2d0 mm/slub.c:4561
   selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
   security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
   tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
   netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
   rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
   __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
   tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
   vfs_ioctl fs/ioctl.c:51 [inline]
   __do_sys_ioctl fs/ioctl.c:874 [inline]
   __se_sys_ioctl fs/ioctl.c:860 [inline]
   __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fd496f4c289
Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89
f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01
f0 ff ff 73 01 c3 48 8b 0d b7 db 2c 00 f7 d8 64 89 01 48
RSP: 002b:00007fd497632e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000603190 RCX: 00007fd496f4c289
RDX: 0000000020000240 RSI: 00000000400454ca RDI: 0000000000000003
RBP: 0000000000603198 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000060319c
R13: 0000000000021000 R14: 0000000000000000 R15: 00007fd497633700
   </TASK>

Allocated by task 25750:
   kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
   kasan_set_track mm/kasan/common.c:46 [inline]
   set_alloc_info mm/kasan/common.c:434 [inline]
   ____kasan_kmalloc mm/kasan/common.c:513 [inline]
   __kasan_kmalloc+0x8d/0xb0 mm/kasan/common.c:522
   kasan_kmalloc include/linux/kasan.h:269 [inline]
   kmem_cache_alloc_trace+0x18a/0x2d0 mm/slub.c:3261
   kmalloc include/linux/slab.h:590 [inline]
   kzalloc include/linux/slab.h:724 [inline]
   selinux_tun_dev_alloc_security+0x50/0x180 security/selinux/hooks.c:5594
   security_tun_dev_alloc_security+0x51/0xb0 security/security.c:2336
   tun_set_iff.constprop.66+0x107f/0x1d10 drivers/net/tun.c:2727
   __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
   tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
   vfs_ioctl fs/ioctl.c:51 [inline]
   __do_sys_ioctl fs/ioctl.c:874 [inline]
   __se_sys_ioctl fs/ioctl.c:860 [inline]
   __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x44/0xae

Freed by task 25750:
   kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
   kasan_set_track+0x25/0x30 mm/kasan/common.c:46
   kasan_set_free_info+0x24/0x40 mm/kasan/generic.c:370
   ____kasan_slab_free mm/kasan/common.c:366 [inline]
   ____kasan_slab_free mm/kasan/common.c:328 [inline]
   __kasan_slab_free+0xe8/0x120 mm/kasan/common.c:374
   kasan_slab_free include/linux/kasan.h:235 [inline]
   slab_free_hook mm/slub.c:1723 [inline]
   slab_free_freelist_hook mm/slub.c:1749 [inline]
   slab_free mm/slub.c:3513 [inline]
   kfree+0xac/0x2d0 mm/slub.c:4561
   selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
   security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
   tun_set_iff.constprop.66+0x9f9/0x1d10 drivers/net/tun.c:2782
   __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
   tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
   vfs_ioctl fs/ioctl.c:51 [inline]
   __do_sys_ioctl fs/ioctl.c:874 [inline]
   __se_sys_ioctl fs/ioctl.c:860 [inline]
   __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff888066b87370
   which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes inside of
   8-byte region [ffff888066b87370, ffff888066b87378)
The buggy address belongs to the page:
page:0000000003b0639d refcount:1 mapcount:0 mapping:0000000000000000
index:0x0 pfn:0x66b87
flags: 0xfffffc0000200(slab|node=0|zone=1|lastcpupid=0x1fffff)
raw: 000fffffc0000200 dead000000000100 dead000000000122 ffff888100042280
raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
   ffff888066b87200: fc fb fc fc fc fc 00 fc fc fc fc fa fc fc fc fc
   ffff888066b87280: fa fc fc fc fc fa fc fc fc fc fb fc fc fc fc fa
  >ffff888066b87300: fc fc fc fc 00 fc fc fc fc fb fc fc fc fc fa fc
                                                               ^
   ffff888066b87380: fc fc fc fa fc fc fc fc 00 fc fc fc fc fa fc fc
   ffff888066b87400: fc fc fa fc fc fc fc fa fc fc fc fc fa fc fc fc
==================================================================

quoted

And why can't security_tun_dev_free_security() handle a NULL value?

security_tun_dev_free_security() could be modified to handle the NULL value.

It looks like a lot of the problem is duplicate unwind.
Why does err_free_flow, err_free_stat etc unwinds need to exist if
the free_netdev is going to do same thing.

Maybe instead do not call security_tun_dev_free_security(tun->security) in err_free_flow if it's going to be done anyway in tun_free_netdev().

George

On Wed, 8 Dec 2021 11:44:02 -0500 George Kennedy wrote:

quoted

It looks like a lot of the problem is duplicate unwind.
Why does err_free_flow, err_free_stat etc unwinds need to exist if
the free_netdev is going to do same thing.  

Maybe instead do not call security_tun_dev_free_security(tun->security) 
in err_free_flow if it's going to be done anyway in tun_free_netdev().

That won't be good either. register_netdevice() has multiple failure
modes, it may or may not call the destructor depending on where it
fails. Either the stuff that destructor undoes needs to be moved to
ndo_init (which is what destructor always pairs with), or you can check
dev->reg_state. If dev->reg_state is NETREG_UNREGISTERING that means
the destructor will be caller later.

The ndo_init way is preferable, just cut and past the appropriate lines
preceding registration into a ndo_init callback.

On 12/8/2021 6:58 PM, Jakub Kicinski wrote:

On Wed, 8 Dec 2021 11:44:02 -0500 George Kennedy wrote:

quoted

quoted

It looks like a lot of the problem is duplicate unwind.
Why does err_free_flow, err_free_stat etc unwinds need to exist if
the free_netdev is going to do same thing.

Maybe instead do not call security_tun_dev_free_security(tun->security)
in err_free_flow if it's going to be done anyway in tun_free_netdev().

That won't be good either. register_netdevice() has multiple failure
modes, it may or may not call the destructor depending on where it
fails. Either the stuff that destructor undoes needs to be moved to
ndo_init (which is what destructor always pairs with), or you can check
dev->reg_state. If dev->reg_state is NETREG_UNREGISTERING that means
the destructor will be caller later.

The ndo_init way is preferable, just cut and past the appropriate lines
preceding registration into a ndo_init callback.

Thank you Jakub,

Looking at other ndo_init's to try and figure out how much before register_netdevice() should go in it.

George