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SubjectKASAN: slab-out-of-bounds Read in fscache_alloc_cookie
From
Hello,

syzbot found the following crash on:

HEAD commit: ca04b3cca11a Merge tag 'armsoc-fixes' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11e382e0400000
kernel config: https://syzkaller.appspot.com/x/.config?x=2ca6c7a31d407f86
dashboard link: https://syzkaller.appspot.com/bug?extid=a95b989b2dde8e806af8
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
userspace arch: i386
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1097c6fc400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=152d29b2400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a95b989b2dde8e806af8@syzkaller.appspotmail.com

sshd (4453) used greatest stack depth: 17048 bytes left
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
==================================================================
BUG: KASAN: slab-out-of-bounds in fscache_set_key fs/fscache/cookie.c:120
[inline]
BUG: KASAN: slab-out-of-bounds in fscache_alloc_cookie+0x7a9/0x880
fs/fscache/cookie.c:171
Read of size 4 at addr ffff8801d3cc8bb4 by task syz-executor907/4466

CPU: 1 PID: 4466 Comm: syz-executor907 Not tainted 4.18.0-rc3+ #40
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+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+0x242/0x2fe mm/kasan/report.c:412
__asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
fscache_set_key fs/fscache/cookie.c:120 [inline]
fscache_alloc_cookie+0x7a9/0x880 fs/fscache/cookie.c:171
__fscache_acquire_cookie+0x230/0xb00 fs/fscache/cookie.c:303
fscache_acquire_cookie include/linux/fscache.h:338 [inline]
v9fs_cache_session_get_cookie+0xc4/0x270 fs/9p/cache.c:73
v9fs_session_init+0x1013/0x1a80 fs/9p/v9fs.c:464
v9fs_mount+0x7c/0x900 fs/9p/vfs_super.c:135
mount_fs+0xae/0x328 fs/super.c:1277
vfs_kern_mount.part.34+0xdc/0x4e0 fs/namespace.c:1037
vfs_kern_mount fs/namespace.c:1027 [inline]
do_new_mount fs/namespace.c:2518 [inline]
do_mount+0x581/0x30e0 fs/namespace.c:2848
__do_compat_sys_mount fs/compat.c:125 [inline]
__se_compat_sys_mount fs/compat.c:92 [inline]
__ia32_compat_sys_mount+0x5d5/0x860 fs/compat.c:92
do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
do_fast_syscall_32+0x34d/0xfb2 arch/x86/entry/common.c:397
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f17cb9
Code: 55 08 8b 88 64 cd ff ff 8b 98 68 cd ff ff 89 c8 85 d2 74 02 89 0a 5b
5d c3 8b 04 24 c3 8b 1c 24 c3 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90
90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000ffafd7dc EFLAGS: 00000286 ORIG_RAX: 0000000000000015
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000020000280
RDX: 00000000200002c0 RSI: 0000000000800000 RDI: 0000000020000340
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 4466:
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
__do_kmalloc mm/slab.c:3718 [inline]
__kmalloc+0x14e/0x760 mm/slab.c:3727
kmalloc include/linux/slab.h:518 [inline]
kzalloc include/linux/slab.h:707 [inline]
fscache_set_key fs/fscache/cookie.c:101 [inline]
fscache_alloc_cookie+0x701/0x880 fs/fscache/cookie.c:171
__fscache_acquire_cookie+0x230/0xb00 fs/fscache/cookie.c:303
fscache_acquire_cookie include/linux/fscache.h:338 [inline]
v9fs_cache_session_get_cookie+0xc4/0x270 fs/9p/cache.c:73
v9fs_session_init+0x1013/0x1a80 fs/9p/v9fs.c:464
v9fs_mount+0x7c/0x900 fs/9p/vfs_super.c:135
mount_fs+0xae/0x328 fs/super.c:1277
vfs_kern_mount.part.34+0xdc/0x4e0 fs/namespace.c:1037
vfs_kern_mount fs/namespace.c:1027 [inline]
do_new_mount fs/namespace.c:2518 [inline]
do_mount+0x581/0x30e0 fs/namespace.c:2848
__do_compat_sys_mount fs/compat.c:125 [inline]
__se_compat_sys_mount fs/compat.c:92 [inline]
__ia32_compat_sys_mount+0x5d5/0x860 fs/compat.c:92
do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
do_fast_syscall_32+0x34d/0xfb2 arch/x86/entry/common.c:397
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

Freed by task 1:
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
__kthread_create_on_node+0x34a/0x4c0 kernel/kthread.c:337
kthread_create_on_node+0xb1/0xe0 kernel/kthread.c:373
cryptomgr_schedule_test crypto/algboss.c:255 [inline]
cryptomgr_notify+0x5ac/0xb90 crypto/algboss.c:276
notifier_call_chain+0x180/0x390 kernel/notifier.c:93
__blocking_notifier_call_chain kernel/notifier.c:317 [inline]
blocking_notifier_call_chain+0x147/0x190 kernel/notifier.c:328
crypto_probing_notify+0x26/0x80 crypto/api.c:254
crypto_wait_for_test+0x42/0xe0 crypto/algapi.c:361
crypto_register_alg+0xc0/0xe0 crypto/algapi.c:392
crypto_register_shash+0x35/0x50 crypto/shash.c:494
crypto_register_shashes+0x5d/0xe0 crypto/shash.c:509
register_sha512_ssse3 arch/x86/crypto/sha512_ssse3_glue.c:136 [inline]
sha512_ssse3_mod_init+0xc4/0x282 arch/x86/crypto/sha512_ssse3_glue.c:316
do_one_initcall+0x127/0x913 init/main.c:884
do_initcall_level init/main.c:952 [inline]
do_initcalls init/main.c:960 [inline]
do_basic_setup init/main.c:978 [inline]
kernel_init_freeable+0x49b/0x58e init/main.c:1135
kernel_init+0x11/0x1b3 init/main.c:1061
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412

The buggy address belongs to the object at ffff8801d3cc8b80
which belongs to the cache kmalloc-64 of size 64
The buggy address is located 52 bytes inside of
64-byte region [ffff8801d3cc8b80, ffff8801d3cc8bc0)
The buggy address belongs to the page:
page:ffffea00074f3200 count:1 mapcount:0 mapping:ffff8801da800340 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea000750d208 ffffea00074b1f08 ffff8801da800340
raw: 0000000000000000 ffff8801d3cc8000 0000000100000020 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801d3cc8a80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff8801d3cc8b00: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ffff8801d3cc8b80: 00 00 00 00 00 00 07 fc fc fc fc fc fc fc fc fc
^
ffff8801d3cc8c00: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
ffff8801d3cc8c80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================


---
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 syzkaller@googlegroups.com.

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syzbot.
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