Re: fs/notify/inotify: slab-out-of-bounds write in strcpy

[Dmitry Vyukov]

On Wed, Apr 12, 2017 at 5:58 AM, Andrew Zhu Aday
<andrew.aday@xxxxxxxxxxxx> wrote:
> Hi all,
>
> Running syzkaller we've found a "slab-out-of-bounds write in strcpy" error.
>
> Using kernel 4.10-rc7 from www.kernel.org/pub/linux/kernel/v4.x/testing/
>
> Unfortunately, I have not been able to generate a reproducible program.
>
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in strcpy+0x30/0x50 lib/string.c:91 at addr
> ffff88003b332e96
> Write of size 1 by task syz-executor2/3247
> CPU: 1 PID: 3247 Comm: syz-executor2 Not tainted 4.10.0-rc7 #3
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> 1.7.5-20140531_083030-gandalf 04/01/2014
> Call Trace:
>  __dump_stack lib/dump_stack.c:15 [inline]
>  dump_stack+0x95/0xe3 lib/dump_stack.c:51
>  kasan_object_err+0x1c/0x70 mm/kasan/report.c:162
>  print_address_description mm/kasan/report.c:200 [inline]
>  kasan_report_error mm/kasan/report.c:289 [inline]
>  kasan_report.part.1+0x20e/0x4e0 mm/kasan/report.c:311
>  kasan_report+0x20/0x30 mm/kasan/report.c:298
>  check_memory_region_inline mm/kasan/kasan.c:315 [inline]
>  __asan_store1+0x4a/0x50 mm/kasan/kasan.c:744
>  strcpy+0x30/0x50 lib/string.c:91
>  inotify_handle_event+0x148/0x260 fs/notify/inotify/inotify_fsnotify.c:109
>  send_to_group fs/notify/fsnotify.c:179 [inline]
>  fsnotify+0x50b/0xb50 fs/notify/fsnotify.c:275
>  __fsnotify_parent+0xeb/0x190 fs/notify/fsnotify.c:112
>  fsnotify_parent include/linux/fsnotify.h:25 [inline]
>  fsnotify_close include/linux/fsnotify.h:240 [inline]
>  __fput+0xfc/0x380 fs/file_table.c:194
>  ____fput+0x15/0x20 fs/file_table.c:244
>  task_work_run+0xcb/0x100 kernel/task_work.c:116
>  tracehook_notify_resume include/linux/tracehook.h:191 [inline]
>  exit_to_usermode_loop+0xc5/0xd0 arch/x86/entry/common.c:160
>  prepare_exit_to_usermode arch/x86/entry/common.c:190 [inline]
>  syscall_return_slowpath+0x128/0x130 arch/x86/entry/common.c:259
>  entry_SYSCALL_64_fastpath+0xab/0xad
> RIP: 0033:0x44e4f9
> RSP: 002b:00007f9fed919b68 EFLAGS: 00000216 ORIG_RAX: 0000000000000003
> RAX: 0000000000000000 RBX: 00000000006f8000 RCX: 000000000044e4f9
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000006
> RBP: 0000000000000033 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000216 R12: 0000000000000006
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> Object at ffff88003b332e60, in cache kmalloc-64 size: 64
> Allocated:
> PID = 3247
>
> [<ffffffff8104ba96>] save_stack_trace+0x16/0x20
> arch/x86/kernel/stacktrace.c:57
>
> [<ffffffff81305916>] save_stack+0x46/0xd0 mm/kasan/kasan.c:502
>
> [<ffffffff81305b9d>] set_track mm/kasan/kasan.c:514 [inline]
> [<ffffffff81305b9d>] kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:605
>
> [<ffffffff81301da5>] __kmalloc+0x115/0x2d0 mm/slub.c:3737
>
> [<ffffffff8139ba74>] kmalloc include/linux/slab.h:495 [inline]
> [<ffffffff8139ba74>] inotify_handle_event+0x84/0x260
> fs/notify/inotify/inotify_fsnotify.c:99
>
> [<ffffffff81397e4b>] send_to_group fs/notify/fsnotify.c:179 [inline]
> [<ffffffff81397e4b>] fsnotify+0x50b/0xb50 fs/notify/fsnotify.c:275
>
> [<ffffffff8139857b>] __fsnotify_parent+0xeb/0x190 fs/notify/fsnotify.c:112
>
> [<ffffffff813191cc>] fsnotify_parent include/linux/fsnotify.h:25 [inline]
> [<ffffffff813191cc>] fsnotify_close include/linux/fsnotify.h:240 [inline]
> [<ffffffff813191cc>] __fput+0xfc/0x380 fs/file_table.c:194
>
> [<ffffffff813194b5>] ____fput+0x15/0x20 fs/file_table.c:244
>
> [<ffffffff810dfdcb>] task_work_run+0xcb/0x100 kernel/task_work.c:116
>
> [<ffffffff810025a5>] tracehook_notify_resume include/linux/tracehook.h:191
> [inline]
> [<ffffffff810025a5>] exit_to_usermode_loop+0xc5/0xd0
> arch/x86/entry/common.c:160
>
> [<ffffffff81003ae8>] prepare_exit_to_usermode arch/x86/entry/common.c:190
> [inline]
> [<ffffffff81003ae8>] syscall_return_slowpath+0x128/0x130
> arch/x86/entry/common.c:259
>
> [<ffffffff822e48bd>] entry_SYSCALL_64_fastpath+0xab/0xad
> Freed:
> PID = 29969
>
> [<ffffffff8104ba96>] save_stack_trace+0x16/0x20
> arch/x86/kernel/stacktrace.c:57
>
> [<ffffffff81305916>] save_stack+0x46/0xd0 mm/kasan/kasan.c:502
>
> [<ffffffff81306183>] set_track mm/kasan/kasan.c:514 [inline]
> [<ffffffff81306183>] kasan_slab_free+0x73/0xc0 mm/kasan/kasan.c:578
>
> [<ffffffff81300a84>] slab_free_hook mm/slub.c:1355 [inline]
> [<ffffffff81300a84>] slab_free_freelist_hook mm/slub.c:1377 [inline]
> [<ffffffff81300a84>] slab_free mm/slub.c:2954 [inline]
> [<ffffffff81300a84>] kfree+0xd4/0x2a0 mm/slub.c:3874
>
> [<ffffffff81410ba7>] free_rb_tree_fname+0x67/0xa0 fs/ext4/dir.c:402
>
> [<ffffffff81410c12>] ext4_htree_free_dir_info fs/ext4/dir.c:424 [inline]
> [<ffffffff81410c12>] ext4_release_dir+0x32/0x50 fs/ext4/dir.c:622
>
> [<ffffffff81319265>] __fput+0x195/0x380 fs/file_table.c:208
>
> [<ffffffff813194b5>] ____fput+0x15/0x20 fs/file_table.c:244
>
> [<ffffffff810dfdcb>] task_work_run+0xcb/0x100 kernel/task_work.c:116
>
> [<ffffffff810025a5>] tracehook_notify_resume include/linux/tracehook.h:191
> [inline]
> [<ffffffff810025a5>] exit_to_usermode_loop+0xc5/0xd0
> arch/x86/entry/common.c:160
>
> [<ffffffff81003ae8>] prepare_exit_to_usermode arch/x86/entry/common.c:190
> [inline]
> [<ffffffff81003ae8>] syscall_return_slowpath+0x128/0x130
> arch/x86/entry/common.c:259
>
> [<ffffffff822e48bd>] entry_SYSCALL_64_fastpath+0xab/0xad
> Memory state around the buggy address:
>  ffff88003b332d80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff88003b332e00: fc fc fc fc fc fc fc fc fc fc fc fc 00 00 00 00
>>ffff88003b332e80: 00 00 06 fc fc fc fc fc fc fc fc fc fc fc fc fc
>                          ^
>  ffff88003b332f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff88003b332f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fb
> ==================================================================

+ inotify_fsnotify.c maintainers

The only explanation I have for the report is that file_name has
changed in between strlen and strcpy. Is it possible under any
circumstances? That would also explain why it is not reproducible.