KASAN: slab-out-of-bounds Read in map_lookup_elem

[syzbot]

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


IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e631b5...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
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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.
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[Daniel Borkmann]

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

[Dmitry Vyukov]

On Sun, Jan 14, 2018 at 1:13 AM, Daniel Borkmann <dan...@iogearbox.net> wrote:
> 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

Thanks.

Let's tell syzbot about this so that it reports bugs in
map_lookup_elem ever again:

#syz fix:
bpf, array: fix overflow in max_entries and undefined behavior in index_mask

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[Eric Biggers]

On Sun, Jan 14, 2018 at 08:23:37AM +0100, 'Dmitry Vyukov' via syzkaller-bugs wrote:
> On Sun, Jan 14, 2018 at 1:13 AM, Daniel Borkmann <dan...@iogearbox.net> wrote:
> > 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
>
> Thanks.
>
> Let's tell syzbot about this so that it reports bugs in
> map_lookup_elem ever again:
>
> #syz fix:
> bpf, array: fix overflow in max_entries and undefined behavior in index_mask

Dmitry, it seems this wasn't recognized because of the line break.

[Dmitry Vyukov]

On Wed, Jan 31, 2018 at 2:46 AM, Eric Biggers <ebig...@gmail.com> wrote:
>> > 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
>>
>> Thanks.
>>
>> Let's tell syzbot about this so that it reports bugs in
>> map_lookup_elem ever again:
>>
>> #syz fix:
>> bpf, array: fix overflow in max_entries and undefined behavior in index_mask
>
> Dmitry, it seems this wasn't recognized because of the line break.
>
> #syz fix: bpf, array: fix overflow in max_entries and undefined behavior in index_mask

Are you sure? It seems that this bug was "closed" on syzbot on Jan 23.
This is a special counter measure against gmail line splitting. If a
line contains only "#syz fix:", then the title is taken from the next
line. We have a test for this:
https://github.com/google/syzkaller/blob/master/pkg/email/parser_test.go#L235

Btw, what do you use to send text emails with long lines?

[Eric Biggers]

Hmm, I see it's closed now. Probably I confused it with the similar report
"KASAN: use-after-free Read in map_lookup_elem".

I'm using mutt to send these emails.

- Eric