[syzbot] KASAN: slab-out-of-bounds Read in __fscache_acquire_volume

syzbot
2022-08-30T00:05:42Z

Hello,

syzbot found the following issue on:

HEAD commit: 8379c0b31fbc Merge tag 'for-6.0-rc3-tag' of git://git.kern..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=12f5306d080000
kernel config: https://syzkaller.appspot.com/x/.config?x=911efaff115942bb
dashboard link: https://syzkaller.appspot.com/bug?extid=a76f6a6e524cf2080aa3
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1552b3ad080000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15b0294d080000

The issue was bisected to:

commit 24e42e32d347f0787a6f99aeb590f3aaa7221093
Author: David Howells <dhowells@redhat.com>
Date: Wed Nov 18 09:06:42 2020 +0000

9p: Use fscache indexing rewrite and reenable caching

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=14660e8b080000
final oops: https://syzkaller.appspot.com/x/report.txt?x=16660e8b080000
console output: https://syzkaller.appspot.com/x/log.txt?x=12660e8b080000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a76f6a6e524cf2080aa3@syzkaller.appspotmail.com
Fixes: 24e42e32d347 ("9p: Use fscache indexing rewrite and reenable caching")

==================================================================
BUG: KASAN: slab-out-of-bounds in memcmp+0x16f/0x1c0 lib/string.c:757
Read of size 8 at addr ffff888016f3aa90 by task syz-executor344/3613

CPU: 0 PID: 3613 Comm: syz-executor344 Not tainted 6.0.0-rc2-syzkaller-00327-g8379c0b31fbc #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:317 [inline]
print_report.cold+0x2ba/0x719 mm/kasan/report.c:433
kasan_report+0xb1/0x1e0 mm/kasan/report.c:495
memcmp+0x16f/0x1c0 lib/string.c:757
memcmp include/linux/fortify-string.h:420 [inline]
fscache_volume_same fs/fscache/volume.c:133 [inline]
fscache_hash_volume fs/fscache/volume.c:171 [inline]
__fscache_acquire_volume+0x76c/0x1080 fs/fscache/volume.c:328
fscache_acquire_volume include/linux/fscache.h:204 [inline]
v9fs_cache_session_get_cookie+0x143/0x240 fs/9p/cache.c:34
v9fs_session_init+0x1166/0x1810 fs/9p/v9fs.c:473
v9fs_mount+0xba/0xc90 fs/9p/vfs_super.c:126
legacy_get_tree+0x105/0x220 fs/fs_context.c:610
vfs_get_tree+0x89/0x2f0 fs/super.c:1530
do_new_mount fs/namespace.c:3040 [inline]
path_mount+0x1326/0x1e20 fs/namespace.c:3370
do_mount fs/namespace.c:3383 [inline]
__do_sys_mount fs/namespace.c:3591 [inline]
__se_sys_mount fs/namespace.c:3568 [inline]
__x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f7d5064b1d9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 14 00 00 90 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 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd1700c028 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ffd1700c060 RCX: 00007f7d5064b1d9
RDX: 0000000020000040 RSI: 0000000020000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000020000200 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000000f4240
R13: 0000000000000000 R14: 00007ffd1700c04c R15: 00007ffd1700c050
</TASK>

Allocated by task 3613:
kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38
kasan_set_track mm/kasan/common.c:45 [inline]
set_alloc_info mm/kasan/common.c:437 [inline]
____kasan_kmalloc mm/kasan/common.c:516 [inline]
____kasan_kmalloc mm/kasan/common.c:475 [inline]
__kasan_kmalloc+0xa9/0xd0 mm/kasan/common.c:525
kmalloc include/linux/slab.h:605 [inline]
kzalloc include/linux/slab.h:733 [inline]
fscache_alloc_volume fs/fscache/volume.c:234 [inline]
__fscache_acquire_volume+0x2c2/0x1080 fs/fscache/volume.c:323
fscache_acquire_volume include/linux/fscache.h:204 [inline]
v9fs_cache_session_get_cookie+0x143/0x240 fs/9p/cache.c:34
v9fs_session_init+0x1166/0x1810 fs/9p/v9fs.c:473
v9fs_mount+0xba/0xc90 fs/9p/vfs_super.c:126
legacy_get_tree+0x105/0x220 fs/fs_context.c:610
vfs_get_tree+0x89/0x2f0 fs/super.c:1530
do_new_mount fs/namespace.c:3040 [inline]
path_mount+0x1326/0x1e20 fs/namespace.c:3370
do_mount fs/namespace.c:3383 [inline]
__do_sys_mount fs/namespace.c:3591 [inline]
__se_sys_mount fs/namespace.c:3568 [inline]
__x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

The buggy address belongs to the object at ffff888016f3aa00
which belongs to the cache kmalloc-192 of size 192
The buggy address is located 144 bytes inside of
192-byte region [ffff888016f3aa00, ffff888016f3aac0)

The buggy address belongs to the physical page:
page:ffffea00005bce80 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x16f3a
flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000200 ffffea00005bd000 dead000000000002 ffff888011841a00
raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 1, tgid 1 (swapper/0), ts 1480756181, free_ts 0
prep_new_page mm/page_alloc.c:2532 [inline]
get_page_from_freelist+0x109b/0x2ce0 mm/page_alloc.c:4283
__alloc_pages+0x1c7/0x510 mm/page_alloc.c:5515
alloc_page_interleave+0x1e/0x200 mm/mempolicy.c:2103
alloc_pages+0x22f/0x270 mm/mempolicy.c:2265
alloc_slab_page mm/slub.c:1824 [inline]
allocate_slab+0x27e/0x3d0 mm/slub.c:1969
new_slab mm/slub.c:2029 [inline]
___slab_alloc+0x7f1/0xe10 mm/slub.c:3031
__slab_alloc.constprop.0+0x4d/0xa0 mm/slub.c:3118
slab_alloc_node mm/slub.c:3209 [inline]
slab_alloc mm/slub.c:3251 [inline]
kmem_cache_alloc_trace+0x323/0x3e0 mm/slub.c:3282
kmalloc include/linux/slab.h:600 [inline]
kzalloc include/linux/slab.h:733 [inline]
call_usermodehelper_setup+0x97/0x340 kernel/umh.c:365
kobject_uevent_env+0xee6/0x1640 lib/kobject_uevent.c:614
kernel_add_sysfs_param kernel/params.c:816 [inline]
param_sysfs_builtin kernel/params.c:851 [inline]
param_sysfs_init+0x367/0x43b kernel/params.c:970
do_one_initcall+0xfe/0x650 init/main.c:1296
do_initcall_level init/main.c:1369 [inline]
do_initcalls init/main.c:1385 [inline]
do_basic_setup init/main.c:1404 [inline]
kernel_init_freeable+0x6b1/0x73a init/main.c:1623
kernel_init+0x1a/0x1d0 init/main.c:1512
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
page_owner free stack trace missing

Memory state around the buggy address:
ffff888016f3a980: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff888016f3aa00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888016f3aa80: 00 00 04 fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff888016f3ab00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888016f3ab80: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================

---
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