KASAN: use-after-free Read in ep_scan_ready_list

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 98be45067040 Add linux-next specific files for 20180711
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10de4efc400000
kernel config: https://syzkaller.appspot.com/x/.config?x=3f3b3673fec35d01
dashboard link: https://syzkaller.appspot.com/bug?extid=78b902c73c69102cb767
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=13d5291c400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16ed430c400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+78b902...@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
IPVS: ftp: loaded support on port[0] = 21
==================================================================
BUG: KASAN: use-after-free in atomic64_read
include/asm-generic/atomic-instrumented.h:27 [inline]
BUG: KASAN: use-after-free in atomic_long_read
include/asm-generic/atomic-long.h:47 [inline]
BUG: KASAN: use-after-free in __mutex_trylock_or_owner
kernel/locking/mutex.c:84 [inline]
BUG: KASAN: use-after-free in __mutex_trylock kernel/locking/mutex.c:125
[inline]
BUG: KASAN: use-after-free in __mutex_lock_common
kernel/locking/mutex.c:927 [inline]
BUG: KASAN: use-after-free in __mutex_lock+0x185/0x1680
kernel/locking/mutex.c:1073
Read of size 8 at addr ffff8801c62d85b8 by task kworker/0:2/2137

CPU: 0 PID: 2137 Comm: kworker/0:2 Not tainted 4.18.0-rc4-next-20180711+ #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: events p9_poll_workfn
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272
atomic64_read include/asm-generic/atomic-instrumented.h:27 [inline]
atomic_long_read include/asm-generic/atomic-long.h:47 [inline]
__mutex_trylock_or_owner kernel/locking/mutex.c:84 [inline]
__mutex_trylock kernel/locking/mutex.c:125 [inline]
__mutex_lock_common kernel/locking/mutex.c:927 [inline]
__mutex_lock+0x185/0x1680 kernel/locking/mutex.c:1073
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1088
ep_scan_ready_list+0xb77/0xf50 fs/eventpoll.c:681
ep_eventpoll_poll+0x192/0x200 fs/eventpoll.c:937
vfs_poll include/linux/poll.h:86 [inline]
p9_fd_poll+0x1ce/0x2b0 net/9p/trans_fd.c:248
p9_poll_mux net/9p/trans_fd.c:617 [inline]
p9_poll_workfn+0x463/0x6d0 net/9p/trans_fd.c:1107
process_one_work+0xc73/0x1ba0 kernel/workqueue.c:2153
worker_thread+0x189/0x13c0 kernel/workqueue.c:2296
kthread+0x345/0x410 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:415

Allocated by task 4472:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
kmem_cache_alloc_trace+0x152/0x780 mm/slab.c:3620
kmalloc include/linux/slab.h:513 [inline]
kzalloc include/linux/slab.h:707 [inline]
ep_alloc fs/eventpoll.c:1016 [inline]
do_epoll_create+0x170/0x5c0 fs/eventpoll.c:1952
__do_sys_epoll_create1 fs/eventpoll.c:1983 [inline]
__se_sys_epoll_create1 fs/eventpoll.c:1981 [inline]
__x64_sys_epoll_create1+0x31/0x40 fs/eventpoll.c:1981
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 4472:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xd9/0x260 mm/slab.c:3813
ep_free+0x273/0x310 fs/eventpoll.c:856
ep_eventpoll_release+0x44/0x60 fs/eventpoll.c:864
__fput+0x35d/0x930 fs/file_table.c:252
____fput+0x15/0x20 fs/file_table.c:288
task_work_run+0x1ec/0x2a0 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0x1b08/0x2750 kernel/exit.c:869
do_group_exit+0x177/0x440 kernel/exit.c:972
get_signal+0x88e/0x1970 kernel/signal.c:2467
do_signal+0x9c/0x21c0 arch/x86/kernel/signal.c:816
exit_to_usermode_loop+0x2e5/0x380 arch/x86/entry/common.c:162
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801c62d8580
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 56 bytes inside of
512-byte region [ffff8801c62d8580, ffff8801c62d8780)
The buggy address belongs to the page:
page:ffffea000718b600 count:1 mapcount:0 mapping:ffff8801da800940 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0006b54dc8 ffffea000764a188 ffff8801da800940
raw: 0000000000000000 ffff8801c62d8080 0000000100000006 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801c62d8480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801c62d8500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801c62d8580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801c62d8600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801c62d8680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a bot. It may contain errors.
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[syzbot]

syzbot suspects this bug was fixed by commit:

commit 430ac66eb4c5b5c4eb846b78ebf65747510b30f1
Author: Tomas Bortoli <tomasb...@gmail.com>
Date: Fri Jul 20 09:27:30 2018 +0000

net/9p/trans_fd.c: fix race-condition by flushing workqueue before the
kfree()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=167fa19ae00000
start commit: 1e09177a Merge tag 'mips_fixes_4.18_3' of git://git.kernel..
git tree: upstream
kernel config: https://syzkaller.appspot.com/x/.config?x=25856fac4e580aa7
dashboard link: https://syzkaller.appspot.com/bug?extid=78b902c73c69102cb767
userspace arch: i386
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=135660c8400000

If the result looks correct, please mark the bug fixed by replying with:

#syz fix: net/9p/trans_fd.c: fix race-condition by flushing workqueue
before the kfree()

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

[syzbot]

> #syz fix: net/9p/trans_fd.c: fix race-condition by flushing workqueue

Your 'fix:' command is accepted, but please keep
syzkall...@googlegroups.com mailing list in CC next time. It serves as
a history of what happened with each bug report. Thank you.

> before the kfree()

[Eric Biggers]