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

From: syzbot
Date: Thu Apr 05 2018 - 13:02:06 EST

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Hello,

syzbot hit the following crash on upstream commit
06dd3dfeea60e2a6457a6aedf97afc8e6d2ba497 (Thu Apr 5 03:07:20 2018 +0000)
Merge tag 'char-misc-4.17-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc
syzbot dashboard link: https://syzkaller.appspot.com/bug?extid=60c837b428dc84e83a93

So far this crash happened 2 times on upstream.
syzkaller reproducer: https://syzkaller.appspot.com/x/repro.syz?id=4920703421775872
Raw console output: https://syzkaller.appspot.com/x/log.txt?id=5627492903682048
Kernel config: https://syzkaller.appspot.com/x/.config?id=216543573824217049
compiler: gcc (GCC) 8.0.1 20180301 (experimental)

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Reported-by: syzbot+60c837b428dc84e83a93@xxxxxxxxxxxxxxxxxxxxxxxxx
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IPVS: ftp: loaded support on port[0] = 21
==================================================================
BUG: KASAN: slab-out-of-bounds in strlen+0x91/0xa0 lib/string.c:482
Read of size 1 at addr ffff8801ac7eb680 by task syz-executor0/4520

CPU: 0 PID: 4520 Comm: syz-executor0 Not tainted 4.16.0+ #1
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+0x1b9/0x29f lib/dump_stack.c:53
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0xac/0x2f5 mm/kasan/report.c:412
__asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
strlen+0x91/0xa0 lib/string.c:482
strlen include/linux/string.h:267 [inline]
getname_kernel+0x24/0x370 fs/namei.c:216
kern_path+0x1e/0x40 fs/namei.c:2397
create_local_trace_uprobe+0x96/0x6e0 kernel/trace/trace_uprobe.c:1357
perf_uprobe_init+0x189/0x260 kernel/trace/trace_event_perf.c:310
perf_uprobe_event_init+0xdb/0x160 kernel/events/core.c:8444
perf_try_init_event+0x137/0x2f0 kernel/events/core.c:9719
perf_init_event kernel/events/core.c:9750 [inline]
perf_event_alloc.part.91+0x1920/0x30a0 kernel/events/core.c:10022
perf_event_alloc kernel/events/core.c:10376 [inline]
SYSC_perf_event_open+0xa8a/0x2fa0 kernel/events/core.c:10477
SyS_perf_event_open+0x35/0x40 kernel/events/core.c:10366
do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4552d9
RSP: 002b:00007f1ec591fc68 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
RAX: ffffffffffffffda RBX: 00007f1ec59206d4 RCX: 00000000004552d9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000002000a000
RBP: 000000000072c010 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000458 R14: 00000000006f98e0 R15: 0000000000000002

Allocated by task 4520:
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:552
kmem_cache_alloc_trace+0x152/0x780 mm/slab.c:3608
kmalloc include/linux/slab.h:512 [inline]
kzalloc include/linux/slab.h:701 [inline]
perf_uprobe_init+0x97/0x260 kernel/trace/trace_event_perf.c:298
perf_uprobe_event_init+0xdb/0x160 kernel/events/core.c:8444
perf_try_init_event+0x137/0x2f0 kernel/events/core.c:9719
perf_init_event kernel/events/core.c:9750 [inline]
perf_event_alloc.part.91+0x1920/0x30a0 kernel/events/core.c:10022
perf_event_alloc kernel/events/core.c:10376 [inline]
SYSC_perf_event_open+0xa8a/0x2fa0 kernel/events/core.c:10477
SyS_perf_event_open+0x35/0x40 kernel/events/core.c:10366
do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 2931:
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
__cache_free mm/slab.c:3486 [inline]
kfree+0xd9/0x260 mm/slab.c:3801
kvfree+0x61/0x70 mm/util.c:438
seq_release fs/seq_file.c:368 [inline]
single_release+0x78/0xb0 fs/seq_file.c:605
close_pdeo.part.2+0x11e/0x420 fs/proc/inode.c:166
close_pdeo+0x173/0x1e0 include/linux/spinlock.h:310
proc_reg_release+0x11b/0x150 fs/proc/inode.c:377
__fput+0x34d/0x890 fs/file_table.c:209
____fput+0x15/0x20 fs/file_table.c:243
task_work_run+0x1e4/0x290 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x2bd/0x310 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
syscall_return_slowpath arch/x86/entry/common.c:265 [inline]
do_syscall_64+0x792/0x9d0 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff8801ac7ea680
which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 0 bytes to the right of
4096-byte region [ffff8801ac7ea680, ffff8801ac7eb680)
The buggy address belongs to the page:
page:ffffea0006b1fa80 count:1 mapcount:0 mapping:ffff8801ac7ea680 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801ac7ea680 0000000000000000 0000000100000001
raw: ffffea0006b04e20 ffff8801dac01a48 ffff8801dac00dc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801ac7eb580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8801ac7eb600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

ffff8801ac7eb680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

^
ffff8801ac7eb700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801ac7eb780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

---
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Next message: Peter Zijlstra: "Re: [PATCH 02/10] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath"
Previous message: Will Deacon: "[PATCH 04/10] locking/qspinlock: Use atomic_cond_read_acquire"
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