Date:   Sun, 14 Jan 2018 01:13:27 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     syzbot <syzbot+e631b5eb810eae08510d@...kaller.appspotmail.com>,
        ast@...nel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: slab-out-of-bounds Read in map_lookup_elem

On 01/13/2018 02:58 AM, syzbot wrote:
> Hello,
> 
> syzkaller hit the following crash on 19d28fbd306e7ae7c1acf05c3e6968b56f0d196b
> git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-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

Fixed here as well:

https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/commit/?id=bbeb6e4323dad9b5e0ee9f60c223dd532e2403b1

> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+e631b5eb810eae08510d@...kaller.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(1515782899.456:8): avc:  denied  { sys_admin } for  pid=3501 comm="syzkaller937663" 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(1515782899.512:9): avc:  denied  { sys_chroot } for  pid=3502 comm="syzkaller937663" 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 map_lookup_elem+0x4dc/0xbd0 kernel/bpf/syscall.c:584
> Read of size 2097153 at addr ffff8801bfc7e690 by task syzkaller937663/3502
> 
> CPU: 0 PID: 3502 Comm: syzkaller937663 Not tainted 4.15.0-rc7+ #185
> 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:252
>  kasan_report_error mm/kasan/report.c:351 [inline]
>  kasan_report+0x25b/0x340 mm/kasan/report.c:409
>  check_memory_region_inline mm/kasan/kasan.c:260 [inline]
>  check_memory_region+0x137/0x190 mm/kasan/kasan.c:267
>  memcpy+0x23/0x50 mm/kasan/kasan.c:302
>  memcpy include/linux/string.h:344 [inline]
>  map_lookup_elem+0x4dc/0xbd0 kernel/bpf/syscall.c:584
>  SYSC_bpf kernel/bpf/syscall.c:1808 [inline]
>  SyS_bpf+0x922/0x4400 kernel/bpf/syscall.c:1782
>  entry_SYSCALL_64_fastpath+0x23/0x9a
> RIP: 0033:0x440ab9
> RSP: 002b:00000000007dff68 EFLAGS: 00000203 ORIG_RAX: 0000000000000141
> RAX: ffffffffffffffda RBX: 00007fffc494ea60 RCX: 0000000000440ab9
> RDX: 0000000000000018 RSI: 0000000020eab000 RDI: 0000000000000001
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000203 R12: 0000000000402290
> R13: 0000000000402320 R14: 0000000000000000 R15: 0000000000000000
> 
> Allocated by task 3502:
>  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:551
>  __do_kmalloc_node mm/slab.c:3672 [inline]
>  __kmalloc_node+0x47/0x70 mm/slab.c:3679
>  kmalloc_node include/linux/slab.h:541 [inline]
>  bpf_map_area_alloc+0x32/0x80 kernel/bpf/syscall.c:123
>  array_map_alloc+0x351/0xa00 kernel/bpf/arraymap.c:96
>  find_and_alloc_map kernel/bpf/syscall.c:105 [inline]
>  map_create kernel/bpf/syscall.c:404 [inline]
>  SYSC_bpf kernel/bpf/syscall.c:1805 [inline]
>  SyS_bpf+0x7f8/0x4400 kernel/bpf/syscall.c:1782
>  entry_SYSCALL_64_fastpath+0x23/0x9a
> 
> Freed by task 1966:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>  set_track mm/kasan/kasan.c:459 [inline]
>  kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
>  __cache_free mm/slab.c:3488 [inline]
>  kfree+0xd6/0x260 mm/slab.c:3803
>  seq_release fs/seq_file.c:366 [inline]
>  single_release+0x80/0xb0 fs/seq_file.c:602
>  __fput+0x327/0x7e0 fs/file_table.c:210
>  ____fput+0x15/0x20 fs/file_table.c:244
>  task_work_run+0x199/0x270 kernel/task_work.c:113
>  tracehook_notify_resume include/linux/tracehook.h:191 [inline]
>  exit_to_usermode_loop+0x296/0x310 arch/x86/entry/common.c:162
>  prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
>  syscall_return_slowpath+0x490/0x550 arch/x86/entry/common.c:264
>  entry_SYSCALL_64_fastpath+0x98/0x9a
> 
> The buggy address belongs to the object at ffff8801bfc7e5c0
>  which belongs to the cache kmalloc-256 of size 256
> The buggy address is located 208 bytes inside of
>  256-byte region [ffff8801bfc7e5c0, ffff8801bfc7e6c0)
> The buggy address belongs to the page:
> page:ffffea0006ff1f80 count:1 mapcount:0 mapping:ffff8801bfc7e0c0 index:0x0
> flags: 0x2fffc0000000100(slab)
> raw: 02fffc0000000100 ffff8801bfc7e0c0 0000000000000000 000000010000000c
> raw: ffffea00070149e0 ffffea0006ff2be0 ffff8801dac007c0 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8801bfc7e580: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
>  ffff8801bfc7e600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> ffff8801bfc7e680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
>                                            ^
>  ffff8801bfc7e700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801bfc7e780: 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.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzkaller@...glegroups.com.
> 
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