KASAN: slab-out-of-bounds Write in pipe_write

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: b94ae8ad Merge tag 'seccomp-v5.5-rc1' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=106a34a2e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=ff560c3de405258c
dashboard link: https://syzkaller.appspot.com/bug?extid=838eb0878ffd51f27c41
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=146a9f86e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1791d82ae00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+838eb0...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in pipe_write+0xe30/0x1000 fs/pipe.c:488
Write of size 8 at addr ffff8880a8399228 by task syz-executor795/9550

CPU: 1 PID: 9550 Comm: syz-executor795 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x197/0x210 lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:634
__asan_report_store8_noabort+0x17/0x20 mm/kasan/generic_report.c:137
pipe_write+0xe30/0x1000 fs/pipe.c:488
call_write_iter include/linux/fs.h:1895 [inline]
new_sync_write+0x4d3/0x770 fs/read_write.c:483
__vfs_write+0xe1/0x110 fs/read_write.c:496
vfs_write+0x268/0x5d0 fs/read_write.c:558
ksys_write+0x220/0x290 fs/read_write.c:611
__do_sys_write fs/read_write.c:623 [inline]
__se_sys_write fs/read_write.c:620 [inline]
__x64_sys_write+0x73/0xb0 fs/read_write.c:620
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4466c9
Code: e8 5c b3 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 0b 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fbd2a7abdb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000006dbc28 RCX: 00000000004466c9
RDX: 00000000fffffef3 RSI: 00000000200001c0 RDI: 0000000000000004
RBP: 00000000006dbc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc2c
R13: 00007ffc2fcd0f6f R14: 00007fbd2a7ac9c0 R15: 20c49ba5e353f7cf

Allocated by task 9552:
save_stack+0x23/0x90 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
__kasan_kmalloc mm/kasan/common.c:510 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:483
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:524
__do_kmalloc mm/slab.c:3655 [inline]
__kmalloc+0x163/0x770 mm/slab.c:3664
kmalloc_array include/linux/slab.h:618 [inline]
kcalloc include/linux/slab.h:629 [inline]
pipe_set_size fs/pipe.c:1143 [inline]
pipe_fcntl+0x3f7/0x8e0 fs/pipe.c:1209
do_fcntl+0x255/0x1030 fs/fcntl.c:417
__do_sys_fcntl fs/fcntl.c:463 [inline]
__se_sys_fcntl fs/fcntl.c:448 [inline]
__x64_sys_fcntl+0x16d/0x1e0 fs/fcntl.c:448
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8880a8399200
which belongs to the cache kmalloc-64 of size 64
The buggy address is located 40 bytes inside of
64-byte region [ffff8880a8399200, ffff8880a8399240)
The buggy address belongs to the page:
page:ffffea0002a0e640 refcount:1 mapcount:0 mapping:ffff8880aa400380
index:0x0
raw: 00fffe0000000200 ffffea0002752548 ffffea00029d3648 ffff8880aa400380
raw: 0000000000000000 ffff8880a8399000 0000000100000020 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a8399100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a8399180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8880a8399200: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc
^
ffff8880a8399280: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff8880a8399300: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================


---
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[syzbot]

syzbot has bisected this bug to:

commit a194dfe6e6f6f7205eea850a420f2bc6a1541209
Author: David Howells <dhow...@redhat.com>
Date: Fri Sep 20 15:32:19 2019 +0000

pipe: Rearrange sequence in pipe_write() to preallocate slot

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=16085abce00000
start commit: b94ae8ad Merge tag 'seccomp-v5.5-rc1' of git://git.kernel...
git tree: upstream
final crash: https://syzkaller.appspot.com/x/report.txt?x=15085abce00000
console output: https://syzkaller.appspot.com/x/log.txt?x=11085abce00000

kernel config: https://syzkaller.appspot.com/x/.config?x=ff560c3de405258c
dashboard link: https://syzkaller.appspot.com/bug?extid=838eb0878ffd51f27c41

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=146a9f86e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1791d82ae00000

Reported-by: syzbot+838eb0...@syzkaller.appspotmail.com
Fixes: a194dfe6e6f6 ("pipe: Rearrange sequence in pipe_write() to
preallocate slot")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[Eric Biggers]

Hi David,

It looks like the 'mask' variable in pipe_write() is not being updated after the
pipe mutex was dropped in pipe_wait(), to take into account the pipe size
possibly having been changed in the mean time.

BTW, I see that the pipe changes were not in linux-next before being sent to
Linus. Please do this next time so that syzbot can find the obvious bugs before
they reach mainline. It's annoying having my system crash on latest mainline
during normal use, due to a bug easily found in < 1 day by an automated system.

- Eric

[David Howells]

Eric Biggers <ebig...@kernel.org> wrote:

> It looks like the 'mask' variable in pipe_write() is not being updated after
> the pipe mutex was dropped in pipe_wait(), to take into account the pipe
> size possibly having been changed in the mean time.

There's that, but not only that. Weirdness ensues if the ring size is 1 -
this may have to do with the mask then being 0.

David