[syzbot] [kernfs?] KASAN: slab-use-after-free Read in kernfs_test_super

syzbot
2023-08-26T16:54:25Z

Hello,

syzbot found the following issue on:

HEAD commit: 28c736b0e92e Add linux-next specific files for 20230822
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=15515d53a80000
kernel config: https://syzkaller.appspot.com/x/.config?x=20999f779fa96017
dashboard link: https://syzkaller.appspot.com/bug?extid=f25c61df1ec3d235d52f
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15783640680000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=164da860680000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/37bc881cd0b2/disk-28c736b0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4512f7892b3d/vmlinux-28c736b0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/052fe1287e05/bzImage-28c736b0.xz

The issue was bisected to:

commit 2c18a63b760a0f68f14cb8bb4c3840bb0b63b73e
Author: Christian Brauner <brauner@kernel.org>
Date: Fri Aug 18 14:00:51 2023 +0000

super: wait until we passed kill super

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=14e6a360680000
final oops: https://syzkaller.appspot.com/x/report.txt?x=16e6a360680000
console output: https://syzkaller.appspot.com/x/log.txt?x=12e6a360680000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f25c61df1ec3d235d52f@syzkaller.appspotmail.com
Fixes: 2c18a63b760a ("super: wait until we passed kill super")

==================================================================
BUG: KASAN: slab-use-after-free in kernfs_test_super+0x122/0x150 fs/kernfs/mount.c:295
Read of size 8 at addr ffff88807249d808 by task syz-executor493/5717

CPU: 1 PID: 5717 Comm: syz-executor493 Not tainted 6.5.0-rc7-next-20230822-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xc4/0x620 mm/kasan/report.c:475
kasan_report+0xda/0x110 mm/kasan/report.c:588
kernfs_test_super+0x122/0x150 fs/kernfs/mount.c:295
sget_fc+0x582/0x9b0 fs/super.c:778
kernfs_get_tree+0x198/0x9a0 fs/kernfs/mount.c:346
sysfs_get_tree+0x41/0x140 fs/sysfs/mount.c:31
vfs_get_tree+0x8c/0x370 fs/super.c:1713
do_new_mount fs/namespace.c:3335 [inline]
path_mount+0x1492/0x1ed0 fs/namespace.c:3662
do_mount fs/namespace.c:3675 [inline]
__do_sys_mount fs/namespace.c:3884 [inline]
__se_sys_mount fs/namespace.c:3861 [inline]
__x64_sys_mount+0x293/0x310 fs/namespace.c:3861
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f126c3d79c9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff40e973e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f126c3d79c9
RDX: 0000000020000300 RSI: 0000000020000080 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 00007fff40e9741c
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fff40e9741c
R13: 0000000000000069 R14: 431bde82d7b634db R15: 00007fff40e97450
</TASK>

Allocated by task 5716:
kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
____kasan_kmalloc mm/kasan/common.c:374 [inline]
__kasan_kmalloc+0xa2/0xb0 mm/kasan/common.c:383
kmalloc include/linux/slab.h:599 [inline]
kzalloc include/linux/slab.h:720 [inline]
kernfs_get_tree+0x78/0x9a0 fs/kernfs/mount.c:337
sysfs_get_tree+0x41/0x140 fs/sysfs/mount.c:31
vfs_get_tree+0x8c/0x370 fs/super.c:1713
do_new_mount fs/namespace.c:3335 [inline]
path_mount+0x1492/0x1ed0 fs/namespace.c:3662
do_mount fs/namespace.c:3675 [inline]
__do_sys_mount fs/namespace.c:3884 [inline]
__se_sys_mount fs/namespace.c:3861 [inline]
__x64_sys_mount+0x293/0x310 fs/namespace.c:3861
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 5053:
kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:522
____kasan_slab_free mm/kasan/common.c:236 [inline]
____kasan_slab_free+0x15b/0x1b0 mm/kasan/common.c:200
kasan_slab_free include/linux/kasan.h:164 [inline]
slab_free_hook mm/slub.c:1800 [inline]
slab_free_freelist_hook+0x114/0x1e0 mm/slub.c:1826
slab_free mm/slub.c:3809 [inline]
__kmem_cache_free+0xb8/0x2f0 mm/slub.c:3822
sysfs_kill_sb+0x21/0x30 fs/sysfs/mount.c:86
deactivate_locked_super+0xa0/0x2d0 fs/super.c:454
deactivate_super+0xde/0x100 fs/super.c:504
cleanup_mnt+0x222/0x3d0 fs/namespace.c:1254
task_work_run+0x14d/0x240 kernel/task_work.c:179
ptrace_notify+0x10c/0x130 kernel/signal.c:2387
ptrace_report_syscall include/linux/ptrace.h:411 [inline]
ptrace_report_syscall_exit include/linux/ptrace.h:473 [inline]
syscall_exit_work kernel/entry/common.c:252 [inline]
syscall_exit_to_user_mode_prepare+0x120/0x220 kernel/entry/common.c:279
__syscall_exit_to_user_mode_work kernel/entry/common.c:284 [inline]
syscall_exit_to_user_mode+0xd/0x60 kernel/entry/common.c:297
do_syscall_64+0x44/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd

The buggy address belongs to the object at ffff88807249d800
which belongs to the cache kmalloc-64 of size 64
The buggy address is located 8 bytes inside of
freed 64-byte region [ffff88807249d800, ffff88807249d840)

The buggy address belongs to the physical page:
page:ffffea0001c92740 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7249d
anon flags: 0xfff00000000800(slab|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000800 ffff888012c41640 ffffea0000a28500 dead000000000005
raw: 0000000000000000 0000000000200020 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 0x12c40(GFP_NOFS|__GFP_NOWARN|__GFP_NORETRY), pid 4493, tgid 4493 (udevd), ts 94419071514, free_ts 94405327131
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x2cf/0x340 mm/page_alloc.c:1530
prep_new_page mm/page_alloc.c:1537 [inline]
get_page_from_freelist+0x10d7/0x31b0 mm/page_alloc.c:3213
__alloc_pages+0x1d0/0x4a0 mm/page_alloc.c:4469
alloc_pages+0x1a9/0x270 mm/mempolicy.c:2298
alloc_slab_page mm/slub.c:1870 [inline]
allocate_slab+0x251/0x380 mm/slub.c:2017
new_slab mm/slub.c:2070 [inline]
___slab_alloc+0x8be/0x1570 mm/slub.c:3223
__slab_alloc.constprop.0+0x56/0xa0 mm/slub.c:3322
__slab_alloc_node mm/slub.c:3375 [inline]
slab_alloc_node mm/slub.c:3468 [inline]
__kmem_cache_alloc_node+0x137/0x350 mm/slub.c:3517
__do_kmalloc_node mm/slab_common.c:1022 [inline]
__kmalloc+0x4f/0x100 mm/slab_common.c:1036
kmalloc include/linux/slab.h:603 [inline]
kzalloc include/linux/slab.h:720 [inline]
tomoyo_encode2+0x100/0x3d0 security/tomoyo/realpath.c:45
tomoyo_encode+0x29/0x50 security/tomoyo/realpath.c:80
tomoyo_realpath_from_path+0x196/0x710 security/tomoyo/realpath.c:283
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_path_perm+0x271/0x450 security/tomoyo/file.c:822
security_inode_getattr+0xf1/0x150 security/security.c:2153
vfs_getattr fs/stat.c:206 [inline]
vfs_statx+0x180/0x430 fs/stat.c:281
vfs_fstatat+0x90/0xb0 fs/stat.c:315
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1130 [inline]
free_unref_page_prepare+0x476/0xa40 mm/page_alloc.c:2342
free_unref_page+0x33/0x3b0 mm/page_alloc.c:2435
mm_free_pgd kernel/fork.c:803 [inline]
__mmdrop+0xd7/0x490 kernel/fork.c:921
mmdrop include/linux/sched/mm.h:54 [inline]
__mmput+0x409/0x4d0 kernel/fork.c:1367
mmput+0x62/0x70 kernel/fork.c:1378
exit_mm kernel/exit.c:567 [inline]
do_exit+0x9b4/0x2a20 kernel/exit.c:861
do_group_exit+0xd4/0x2a0 kernel/exit.c:1024
__do_sys_exit_group kernel/exit.c:1035 [inline]
__se_sys_exit_group kernel/exit.c:1033 [inline]
__x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1033
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Memory state around the buggy address:
ffff88807249d700: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff88807249d780: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff88807249d800: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
^
ffff88807249d880: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff88807249d900: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================

---
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