Re: KASAN: use-after-free Write in array_map_update_elem

[Daniel Borkmann]

On 01/15/2018 04:07 PM, Dmitry Vyukov wrote:
> On Mon, Jan 15, 2018 at 3:58 PM, syzbot
> <syzbot+a2215ab5e92b3bb1c95f@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>> Hello,
>>
>> syzkaller hit the following crash on
>> 8418f88764046d0e8ca6a3c04a69a0e57189aa1e
>> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
>> compiler: gcc (GCC) 7.1.1 20170620
>> .config is attached
>> Raw console output is attached.
>> C reproducer is attached
>> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
>> for information about syzkaller reproducers
>>
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+a2215ab5e92b3bb1c95f@xxxxxxxxxxxxxxxxxxxxxxxxx
>> 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(1515680378.393:8): avc:  denied  { sys_admin } for
>> pid=3508 comm="syzkaller203412" capability=21
>> scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
>> tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=cap_userns
>> permissive=1
>> audit: type=1400 audit(1515680378.446:9): avc:  denied  { sys_chroot } for
>> pid=3509 comm="syzkaller203412" capability=18
>> scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
>> tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=cap_userns
>> permissive=1
>> ==================================================================
>> BUG: KASAN: use-after-free in memcpy include/linux/string.h:344 [inline]
>> BUG: KASAN: use-after-free in array_map_update_elem+0x197/0x240
>> kernel/bpf/arraymap.c:249
>> Write of size 1 at addr ffff8801cb125bc0 by task syzkaller203412/3509
>>
>> CPU: 1 PID: 3509 Comm: syzkaller203412 Not tainted 4.15.0-rc7-next-20180111+
>> #94
>> 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+0x194/0x257 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
>>  check_memory_region_inline mm/kasan/kasan.c:260 [inline]
>>  check_memory_region+0x137/0x190 mm/kasan/kasan.c:267
>>  memcpy+0x37/0x50 mm/kasan/kasan.c:303
>>  memcpy include/linux/string.h:344 [inline]
>>  array_map_update_elem+0x197/0x240 kernel/bpf/arraymap.c:249
>>  map_update_elem kernel/bpf/syscall.c:687 [inline]
>>  SYSC_bpf kernel/bpf/syscall.c:1811 [inline]
>>  SyS_bpf+0x32df/0x4400 kernel/bpf/syscall.c:1782
>>  entry_SYSCALL_64_fastpath+0x29/0xa0
>> RIP: 0033:0x440ac9
>> RSP: 002b:00000000007dff68 EFLAGS: 00000203 ORIG_RAX: 0000000000000141
>> RAX: ffffffffffffffda RBX: 00007ffe6a583b10 RCX: 0000000000440ac9
>> RDX: 0000000000000020 RSI: 0000000020eaf000 RDI: 0000000000000002
>> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000203 R12: 00000000004022a0
>> R13: 0000000000402330 R14: 0000000000000000 R15: 0000000000000000
>>
>> Allocated by task 3071:
>>  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
>>  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
>>  kmem_cache_alloc+0x12e/0x760 mm/slab.c:3541
>>  getname_flags+0xcb/0x580 fs/namei.c:138
>>  user_path_at_empty+0x2d/0x50 fs/namei.c:2587
>>  user_path_at include/linux/namei.h:57 [inline]
>>  SYSC_faccessat fs/open.c:384 [inline]
>>  SyS_faccessat fs/open.c:353 [inline]
>>  SYSC_access fs/open.c:431 [inline]
>>  SyS_access+0x22c/0x6a0 fs/open.c:429
>>  entry_SYSCALL_64_fastpath+0x29/0xa0
>>
>> Freed by task 3071:
>>  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]
>>  kmem_cache_free+0x86/0x2b0 mm/slab.c:3743
>>  putname+0xee/0x130 fs/namei.c:258
>>  filename_lookup+0x315/0x500 fs/namei.c:2342
>>  user_path_at_empty+0x40/0x50 fs/namei.c:2587
>>  user_path_at include/linux/namei.h:57 [inline]
>>  SYSC_faccessat fs/open.c:384 [inline]
>>  SyS_faccessat fs/open.c:353 [inline]
>>  SYSC_access fs/open.c:431 [inline]
>>  SyS_access+0x22c/0x6a0 fs/open.c:429
>>  entry_SYSCALL_64_fastpath+0x29/0xa0
>>
>> The buggy address belongs to the object at ffff8801cb124e40
>>  which belongs to the cache names_cache of size 4096
>> The buggy address is located 3456 bytes inside of
>>  4096-byte region [ffff8801cb124e40, ffff8801cb125e40)
>> The buggy address belongs to the page:
>> page:ffffea00072c4900 count:1 mapcount:0 mapping:ffff8801cb124e40 index:0x0
>> compound_mapcount: 0
>> flags: 0x2fffc0000008100(slab|head)
>> raw: 02fffc0000008100 ffff8801cb124e40 0000000000000000 0000000100000001
>> raw: ffffea000729bc20 ffffea000729bca0 ffff8801dae30600 0000000000000000
>> page dumped because: kasan: bad access detected
>>
>> Memory state around the buggy address:
>>  ffff8801cb125a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>  ffff8801cb125b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>
>>> ffff8801cb125b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>
>>                                            ^
>>  ffff8801cb125c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>  ffff8801cb125c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ==================================================================
> 
> 
> This is:
> 
> #syz fix:
> bpf, array: fix overflow in max_entries and undefined behavior in index_mask
> 
> right?

Yes, also correct. I just checked out both and the above linux-next tree
doesn't have that fix included as well.