[syzbot] [gfs2?] KASAN: null-ptr-deref Read in gfs2_drop_inode

Hello,

syzbot found the following issue on:

HEAD commit: 176e917e010c Add linux-next specific files for 20250523
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=135065f4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e7902c752bef748
dashboard link: https://syzkaller.appspot.com/bug?extid=b12826218502df019f9d
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=151759f4580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16b9c5f4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5f7692c642fa/disk-176e917e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/057a442d42d0/vmlinux-176e917e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8f8ebdb4dd96/bzImage-176e917e.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/0e694bf0a04e/mount_0.gz
fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=16e42170580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:68 [inline]
BUG: KASAN: null-ptr-deref in _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
BUG: KASAN: null-ptr-deref in gfs2_drop_inode+0x20c/0x3a0 fs/gfs2/super.c:1052
Read of size 8 at addr 00000000000000a8 by task syz-executor628/5863

CPU: 0 UID: 0 PID: 5863 Comm: syz-executor628 Not tainted 6.15.0-rc7-next-20250523-syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
kasan_report+0x118/0x150 mm/kasan/report.c:634
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x2b0/0x2c0 mm/kasan/generic.c:189
instrument_atomic_read include/linux/instrumented.h:68 [inline]
_test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
gfs2_drop_inode+0x20c/0x3a0 fs/gfs2/super.c:1052
iput_final fs/inode.c:1868 [inline]
iput+0x45d/0x9d0 fs/inode.c:1924
gfs2_fill_super+0x1418/0x2010 fs/gfs2/ops_fstype.c:1314
get_tree_bdev_flags+0x40b/0x4d0 fs/super.c:1679
gfs2_get_tree+0x51/0x1e0 fs/gfs2/ops_fstype.c:1333
vfs_get_tree+0x92/0x2b0 fs/super.c:1802
do_new_mount+0x24a/0xa40 fs/namespace.c:3869
do_mount fs/namespace.c:4206 [inline]
__do_sys_mount fs/namespace.c:4417 [inline]
__se_sys_mount+0x317/0x410 fs/namespace.c:4394
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f219bad284a
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 6e 07 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 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:00007ffdb657b2f8 EFLAGS: 00000282 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f219bad284a
RDX: 0000200000021140 RSI: 0000200000021180 RDI: 00007ffdb657b350
RBP: 0000000000000004 R08: 00007ffdb657b390 R09: 0000000000021135
R10: 0000000000000000 R11: 0000000000000282 R12: 0000000001000000
R13: 00007ffdb657b390 R14: 0000200000021180 R15: 0000000000000003
</TASK>
==================================================================


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syzbot has bisected this issue to:

commit ae9f3bd8259a0a8f67be2420e66bb05fbb95af48
Author: Andreas Gruenbacher <[email protected]>
Date: Sat Apr 5 22:31:37 2025 +0000

gfs2: replace sd_aspace with sd_inode

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1042cdf4580000
start commit: 176e917e010c Add linux-next specific files for 20250523
git tree: linux-next
final oops: https://syzkaller.appspot.com/x/report.txt?x=1242cdf4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=1442cdf4580000
Reported-by: [email protected]
Fixes: ae9f3bd8259a ("gfs2: replace sd_aspace with sd_inode")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

For archival purposes, forwarding an incoming command email to
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***

Subject: Re: [syzbot] [gfs2?] KASAN: null-ptr-deref Read in gfs2_drop_inode
Author: [email protected]

#syz test:
git://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2.git for-next

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: [email protected]
Tested-by: [email protected]

Tested on:

commit: 9126d275 gfs2: Don't clear sb->s_fs_info in gfs2_sys_f..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2.git for-next
console output: https://syzkaller.appspot.com/x/log.txt?x=169bf00c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=eeb82b5d1d67d535
Note: no patches were applied.
Note: testing is done by a robot and is best-effort only.