Re: [PATCH] tun: avoid double free in tun_free_netdev
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From: Stephen Hemminger <stephen@networkplumber.org>
Date: 2021-12-08 16:36:20
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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.