[+ppp list and maintainer]

On Wed, Feb 28, 2018 at 08:59:02AM -0800, syzbot wrote:

Hello,

syzbot hit the following crash on upstream commit
f3afe530d644488a074291da04a69a296ab63046 (Tue Feb 27 22:02:39 2018 +0000)
Merge branch 'fixes-v4.16-rc4' of
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security

So far this crash happened 3 times on upstream.
C reproducer is attached.
syzkaller reproducer is attached.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+16363c99d4134717c05b@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
details.
If you forward the report, please keep this part and the footer.

audit: type=1400 audit(1519800493.311:7): avc:  denied  { map } for
pid=4238 comm="syzkaller305740" path="/root/syzkaller305740266" dev="sda1"
ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
==================================================================
BUG: KASAN: use-after-free in __lock_acquire+0x3d4d/0x3e00
kernel/locking/lockdep.c:3310
Read of size 8 at addr ffff8801afa039c0 by task syzkaller305740/4238

CPU: 1 PID: 4238 Comm: syzkaller305740 Not tainted 4.16.0-rc3+ #332
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x24d lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report+0x23b/0x360 mm/kasan/report.c:412
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 __lock_acquire+0x3d4d/0x3e00 kernel/locking/lockdep.c:3310
 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x96/0xc0 kernel/locking/spinlock.c:152
 remove_wait_queue+0x81/0x350 kernel/sched/wait.c:50
 ep_remove_wait_queue fs/eventpoll.c:596 [inline]
 ep_unregister_pollwait.isra.7+0x18c/0x590 fs/eventpoll.c:614
 ep_free+0x13f/0x320 fs/eventpoll.c:832
 ep_eventpoll_release+0x44/0x60 fs/eventpoll.c:864
 __fput+0x327/0x7e0 fs/file_table.c:209
 ____fput+0x15/0x20 fs/file_table.c:243
 task_work_run+0x199/0x270 kernel/task_work.c:113
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0x9bb/0x1ad0 kernel/exit.c:865
 do_group_exit+0x149/0x400 kernel/exit.c:968
 SYSC_exit_group kernel/exit.c:979 [inline]
 SyS_exit_group+0x1d/0x20 kernel/exit.c:977
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x43e958
RSP: 002b:00007ffe63a11468 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043e958
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004be300 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 00000000004002c8 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006cc160 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 4238:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:552
 __do_kmalloc_node mm/slab.c:3669 [inline]
 __kmalloc_node+0x47/0x70 mm/slab.c:3676
 kmalloc_node include/linux/slab.h:554 [inline]
 kvmalloc_node+0x99/0xd0 mm/util.c:419
 kvmalloc include/linux/mm.h:541 [inline]
 kvzalloc include/linux/mm.h:549 [inline]
 alloc_netdev_mqs+0x16d/0xfb0 net/core/dev.c:8299
 ppp_create_interface drivers/net/ppp/ppp_generic.c:3018 [inline]
 ppp_unattached_ioctl drivers/net/ppp/ppp_generic.c:866 [inline]
 ppp_ioctl+0x1715/0x2a50 drivers/net/ppp/ppp_generic.c:602
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 4238:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
 __cache_free mm/slab.c:3485 [inline]
 kfree+0xd9/0x260 mm/slab.c:3800
 kvfree+0x36/0x60 mm/util.c:438
 netdev_freemem+0x4c/0x60 net/core/dev.c:8253
 netdev_release+0x10a/0x160 net/core/net-sysfs.c:1502
 device_release+0x7c/0x210 drivers/base/core.c:814
 kobject_cleanup lib/kobject.c:646 [inline]
 kobject_release lib/kobject.c:675 [inline]
 kref_put include/linux/kref.h:70 [inline]
 kobject_put+0x14c/0x250 lib/kobject.c:692
 put_device+0x20/0x30 drivers/base/core.c:1931
 free_netdev+0x2f5/0x400 net/core/dev.c:8410
 ppp_destroy_interface+0x2bc/0x390 drivers/net/ppp/ppp_generic.c:3100
 ppp_release+0x12b/0x1a0 drivers/net/ppp/ppp_generic.c:415
 ppp_ioctl+0x3b1/0x2a50 drivers/net/ppp/ppp_generic.c:628
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff8801afa02e40
 which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 2944 bytes inside of
 4096-byte region [ffff8801afa02e40, ffff8801afa03e40)
The buggy address belongs to the page:
page:ffffea0006be8080 count:1 mapcount:0 mapping:ffff8801afa02e40 index:0x0
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801afa02e40 0000000000000000 0000000100000001
raw: ffffea0006bee220 ffffea0006bee7a0 ffff8801dac00dc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801afa03880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801afa03900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

quoted

ffff8801afa03980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

                                           ^
 ffff8801afa03a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801afa03a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a dumb bot. It may contain errors.
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This is a bug in ppp_generic.c; it still happens on Linus' tree and it's easily
reproducible, see program below.  The bug is that the PPPIOCDETACH ioctl doesn't
consider that the file can still be attached to epoll instances even when
->f_count == 1.  Also, the reproducer doesn't test this but I think ppp_poll(),
ppp_read(), and ppp_write() can all race with PPPIOCDETACH, causing
use-after-frees as well.  Any chance that PPPIOCDETACH can simply be removed,
given that it's apparently been "deprecated" for 16 years?  Does anyone use it?

	#include <fcntl.h>
	#include <linux/ppp-ioctl.h>
	#include <sys/epoll.h>
	#include <sys/ioctl.h>

	int main()
	{
		int pppfd, epfd, unit = 0;
		struct epoll_event event = { 0 };

		pppfd = open("/dev/ppp", O_RDONLY);
		ioctl(pppfd, PPPIOCNEWUNIT, &unit);
		epfd = epoll_create(0x2000);
		epoll_ctl(epfd, EPOLL_CTL_ADD, pppfd, &event);
		ioctl(pppfd, PPPIOCDETACH, &unit);
	}

- Eric