KASAN: use-after-free Read in relay_switch_subbuf

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: ddef1e8e Linux 4.14.151
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16b3a2dce00000
kernel config: https://syzkaller.appspot.com/x/.config?x=a2b317f0c5f02ed3
dashboard link: https://syzkaller.appspot.com/bug?extid=3905118b6e6567443ca7
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+390511...@syzkaller.appspotmail.com

audit: type=1804 audit(1572971752.565:647): pid=22999 uid=0 auid=4294967295
ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
op="invalid_pcr" cause="open_writers" comm="syz-executor.5"
name="/root/syzkaller-testdir003095837/syzkaller.bsleOH/751/memory.events"
dev="sda1" ino=16763 res=1
==================================================================
BUG: KASAN: use-after-free in relay_switch_subbuf+0x87c/0x8e0
kernel/relay.c:754
Read of size 8 at addr ffff888087a58358 by task kworker/0:0/21412

CPU: 0 PID: 21412 Comm: kworker/0:0 Not tainted 4.14.151 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: events __blk_release_queue
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x138/0x197 lib/dump_stack.c:53
print_address_description.cold+0x7c/0x1dc mm/kasan/report.c:252
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report mm/kasan/report.c:409 [inline]
kasan_report.cold+0xa9/0x2af mm/kasan/report.c:393
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
relay_switch_subbuf+0x87c/0x8e0 kernel/relay.c:754
relay_flush kernel/relay.c:882 [inline]
relay_flush+0x1ae/0x270 kernel/relay.c:866
blk_trace_startstop+0x203/0x5c0 kernel/trace/blktrace.c:657
blk_trace_shutdown+0x47/0x60 kernel/trace/blktrace.c:727
__blk_release_queue+0x22e/0x4d0 block/blk-sysfs.c:830
process_one_work+0x863/0x1600 kernel/workqueue.c:2114
worker_thread+0x5d9/0x1050 kernel/workqueue.c:2248
kthread+0x319/0x430 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404

Allocated by task 22996:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x45/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc mm/kasan/kasan.c:551 [inline]
kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:529
kasan_slab_alloc+0xf/0x20 mm/kasan/kasan.c:489
kmem_cache_alloc+0x12e/0x780 mm/slab.c:3552
__d_alloc+0x2d/0x9f0 fs/dcache.c:1623
d_alloc+0x4d/0x270 fs/dcache.c:1710
__lookup_hash fs/namei.c:1570 [inline]
__lookup_hash+0x58/0x180 fs/namei.c:1562
lookup_one_len+0x27b/0x3a0 fs/namei.c:2538
start_creating fs/debugfs/inode.c:314 [inline]
start_creating+0xa6/0x1b0 fs/debugfs/inode.c:290
__debugfs_create_file+0x53/0x3d0 fs/debugfs/inode.c:353
debugfs_create_file+0x5a/0x70 fs/debugfs/inode.c:404
blk_create_buf_file_callback+0x33/0x40 kernel/trace/blktrace.c:445
relay_create_buf_file+0xf1/0x160 kernel/relay.c:427
relay_open_buf.part.0+0x6a9/0x9e0 kernel/relay.c:456
relay_open_buf kernel/relay.c:448 [inline]
relay_open kernel/relay.c:598 [inline]
relay_open+0x4e7/0x920 kernel/relay.c:562
do_blk_trace_setup+0x3ca/0xb10 kernel/trace/blktrace.c:533
blk_trace_setup+0xbd/0x140 kernel/trace/blktrace.c:579
blk_trace_ioctl+0x147/0x270 kernel/trace/blktrace.c:694
blkdev_ioctl+0x100/0x1860 block/ioctl.c:580
block_ioctl+0xde/0x120 fs/block_dev.c:1881
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
kobject: 'loop1' (ffff8880a4914de0): fill_kobj_path: path
= '/devices/virtual/block/loop1'

Freed by task 1402:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x45/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_slab_free+0x75/0xc0 mm/kasan/kasan.c:524
__cache_free mm/slab.c:3496 [inline]
kmem_cache_free+0x83/0x2b0 mm/slab.c:3758
__d_free+0x20/0x30 fs/dcache.c:270
__rcu_reclaim kernel/rcu/rcu.h:195 [inline]
rcu_do_batch kernel/rcu/tree.c:2699 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:2962 [inline]
__rcu_process_callbacks kernel/rcu/tree.c:2929 [inline]
rcu_process_callbacks+0x7b8/0x12b0 kernel/rcu/tree.c:2946
kobject: 'loop3' (ffff8880a498eee0): kobject_uevent_env
__do_softirq+0x244/0x9a0 kernel/softirq.c:288

The buggy address belongs to the object at ffff888087a58300
which belongs to the cache dentry of size 288
The buggy address is located 88 bytes inside of
288-byte region [ffff888087a58300, ffff888087a58420)
The buggy address belongs to the page:
page:ffffea00021e9600 count:1 mapcount:0 mapping:ffff888087a58040 index:0x0
flags: 0x1fffc0000000100(slab)
raw: 01fffc0000000100 ffff888087a58040 0000000000000000 000000010000000b
raw: ffffea000268aca0 ffffea00021e28e0 ffff88821f8b5680 0000000000000000
kobject: 'loop3' (ffff8880a498eee0): fill_kobj_path: path
= '/devices/virtual/block/loop3'
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888087a58200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888087a58280: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
> ffff888087a58300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888087a58380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888087a58400: fb fb fb fb fc fc fc fc fc fc fc fc 00 00 00 00
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
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[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit: ddef1e8e Linux 4.14.151
git tree: linux-4.14.y

console output: https://syzkaller.appspot.com/x/log.txt?x=1231a77ce00000

kernel config: https://syzkaller.appspot.com/x/.config?x=a2b317f0c5f02ed3
dashboard link: https://syzkaller.appspot.com/bug?extid=3905118b6e6567443ca7
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11a59392e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=163ed6ece00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+390511...@syzkaller.appspotmail.com

devpts: called with bogus options
devpts: called with bogus options
relay: one or more items not logged [item size (56) > sub-buffer size (9)]
devpts: called with bogus options

==================================================================
BUG: KASAN: use-after-free in relay_switch_subbuf+0x87c/0x8e0
kernel/relay.c:754

Read of size 8 at addr ffff88809a3d6778 by task kworker/0:2/2601

CPU: 0 PID: 2601 Comm: kworker/0:2 Not tainted 4.14.151 #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: events __blk_release_queue
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x138/0x197 lib/dump_stack.c:53
print_address_description.cold+0x7c/0x1dc mm/kasan/report.c:252
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report mm/kasan/report.c:409 [inline]
kasan_report.cold+0xa9/0x2af mm/kasan/report.c:393
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
relay_switch_subbuf+0x87c/0x8e0 kernel/relay.c:754
relay_flush kernel/relay.c:882 [inline]
relay_flush+0x1ae/0x270 kernel/relay.c:866
blk_trace_startstop+0x203/0x5c0 kernel/trace/blktrace.c:657
blk_trace_shutdown+0x47/0x60 kernel/trace/blktrace.c:727
__blk_release_queue+0x22e/0x4d0 block/blk-sysfs.c:830
process_one_work+0x863/0x1600 kernel/workqueue.c:2114
worker_thread+0x5d9/0x1050 kernel/workqueue.c:2248
kthread+0x319/0x430 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404

Allocated by task 6850:

Freed by task 7:

save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x45/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_slab_free+0x75/0xc0 mm/kasan/kasan.c:524
__cache_free mm/slab.c:3496 [inline]
kmem_cache_free+0x83/0x2b0 mm/slab.c:3758
__d_free+0x20/0x30 fs/dcache.c:270
__rcu_reclaim kernel/rcu/rcu.h:195 [inline]
rcu_do_batch kernel/rcu/tree.c:2699 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:2962 [inline]
__rcu_process_callbacks kernel/rcu/tree.c:2929 [inline]
rcu_process_callbacks+0x7b8/0x12b0 kernel/rcu/tree.c:2946

__do_softirq+0x244/0x9a0 kernel/softirq.c:288

The buggy address belongs to the object at ffff88809a3d6720

which belongs to the cache dentry of size 288
The buggy address is located 88 bytes inside of

288-byte region [ffff88809a3d6720, ffff88809a3d6840)

The buggy address belongs to the page:

page:ffffea000268f580 count:1 mapcount:0 mapping:ffff88809a3d6040
index:0xffff88809a3d6300
flags: 0x1fffc0000000100(slab)
raw: 01fffc0000000100 ffff88809a3d6040 ffff88809a3d6300 0000000100000008
raw: ffffea000251b0a0 ffffea000251a9e0 ffff88821f8b5680 0000000000000000

page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff88809a3d6600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809a3d6680: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
> ffff88809a3d6700: fc fc fc fc fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88809a3d6780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809a3d6800: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================