Re: KASAN: slab-out-of-bounds 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+23dc48712d6941968d1f@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>> Hello,
>>
>> syzkaller hit the following crash on
>> 4147d50978df60f34d444c647dde9e5b34a4315e
>> git://git.cmpxchg.org/linux-mmots.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+23dc48712d6941968d1f@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(1515679662.716:8): avc:  denied  { sys_admin } for
>> pid=3485 comm="syzkaller377846" 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(1515679662.770:9): avc:  denied  { sys_chroot } for
>> pid=3486 comm="syzkaller377846" 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: slab-out-of-bounds in memcpy include/linux/string.h:344 [inline]
>> BUG: KASAN: slab-out-of-bounds in array_map_update_elem+0x197/0x240
>> kernel/bpf/arraymap.c:249
>> Write of size 1 at addr ffff8801cb0a3900 by task syzkaller377846/3486
>>
>> CPU: 1 PID: 3486 Comm: syzkaller377846 Not tainted 4.15.0-rc7-mm1+ #53
>> 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: 00007ffc88b23300 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 3072:
>>  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_kernel+0x54/0x340 fs/namei.c:218
>>  open_exec+0x17/0x60 fs/exec.c:877
>>  load_elf_binary+0x1348/0x4c10 fs/binfmt_elf.c:780
>>  search_binary_handler+0x142/0x6b0 fs/exec.c:1639
>>  exec_binprm fs/exec.c:1681 [inline]
>>  do_execveat_common.isra.30+0x1711/0x22a0 fs/exec.c:1803
>>  do_execve fs/exec.c:1848 [inline]
>>  SYSC_execve fs/exec.c:1929 [inline]
>>  SyS_execve+0x39/0x50 fs/exec.c:1924
>>  do_syscall_64+0x273/0x920 arch/x86/entry/common.c:285
>>  return_from_SYSCALL_64+0x0/0x75
>>
>> Freed by task 3072:
>>  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
>>  open_exec+0x41/0x60 fs/exec.c:882
>>  load_elf_binary+0x1348/0x4c10 fs/binfmt_elf.c:780
>>  search_binary_handler+0x142/0x6b0 fs/exec.c:1639
>>  exec_binprm fs/exec.c:1681 [inline]
>>  do_execveat_common.isra.30+0x1711/0x22a0 fs/exec.c:1803
>>  do_execve fs/exec.c:1848 [inline]
>>  SYSC_execve fs/exec.c:1929 [inline]
>>  SyS_execve+0x39/0x50 fs/exec.c:1924
>>  do_syscall_64+0x273/0x920 arch/x86/entry/common.c:285
>>  return_from_SYSCALL_64+0x0/0x75
>>
>> The buggy address belongs to the object at ffff8801cb0a2380
>>  which belongs to the cache names_cache of size 4096
>> The buggy address is located 1408 bytes to the right of
>>  4096-byte region [ffff8801cb0a2380, ffff8801cb0a3380)
>> The buggy address belongs to the page:
>> page:ffffea00072c2880 count:1 mapcount:0 mapping:ffff8801cb0a2380 index:0x0
>> compound_mapcount: 0
>> flags: 0x2fffc0000008100(slab|head)
>> raw: 02fffc0000008100 ffff8801cb0a2380 0000000000000000 0000000100000001
>> raw: ffffea00072c2920 ffffea00072b95a0 ffff8801dae30600 0000000000000000
>> page dumped because: kasan: bad access detected
>>
>> Memory state around the buggy address:
>>  ffff8801cb0a3800: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>  ffff8801cb0a3880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>>
>>> ffff8801cb0a3900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>
>>                    ^
>>  ffff8801cb0a3980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>  ffff8801cb0a3a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>> ==================================================================
> 
> This is:
> 
> #syz fix:
> bpf, array: fix overflow in max_entries and undefined behavior in index_mask
> 
> right?

Yes, correct.