[syzbot] [gfs2?] general protection fault in _find_first_zero_bit

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 51cb1aa1250c Merge tag 'loongarch-7.2' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10748efa580000
kernel config: https://syzkaller.appspot.com/x/.config?x=86ba763b42fa66a
dashboard link: https://syzkaller.appspot.com/bug?extid=cb79de2cc8b76fbf474f
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12b7c246580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1205b6b1580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/edf195a1627e/disk-51cb1aa1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e282a4f3a85b/vmlinux-51cb1aa1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a485374265d8/bzImage-51cb1aa1.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/82f270d69c7c/mount_0.gz
fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=17b48efa580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cb79de...@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 UID: 0 PID: 5755 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:_find_first_zero_bit+0x29/0xb0 lib/find_bit.c:149
Code: 90 f3 0f 1e fa 41 57 41 56 41 55 41 54 53 48 85 f6 74 46 48 89 f3 49 89 fe 49 bf 00 00 00 00 00 fc ff df 48 89 f8 48 c1 e8 03 <42> 80 3c 38 00 74 08 4c 89 f7 e8 b8 55 7c fd 49 8b 06 48 83 f8 ff
RSP: 0018:ffffc9000365f6c0 EFLAGS: 00010256
RAX: 0000000000000000 RBX: 000000000000f800 RCX: 0000000000000000
RDX: ffff888034374c40 RSI: 000000000000f800 RDI: 0000000000000000
RBP: dffffc0000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520006cbecc R12: ffff888058d1d3f0
R13: ffff888034374c38 R14: 0000000000000000 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff888125223000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8b8a06ea00 CR3: 000000000e746000 CR4: 0000000000350ef0
Call Trace:
<TASK>
find_first_zero_bit include/linux/find.h:391 [inline]
slot_get fs/gfs2/quota.c:355 [inline]
qdsb_get+0x133/0x340 fs/gfs2/quota.c:522
gfs2_quota_hold+0x191/0x5c0 fs/gfs2/quota.c:606
gfs2_dinode_dealloc+0x176/0x3f0 fs/gfs2/inode.c:488
evict_unlinked_inode fs/gfs2/super.c:1329 [inline]
gfs2_evict_inode+0x11cd/0x1400 fs/gfs2/super.c:1479
evict+0x624/0xb50 fs/inode.c:825
gfs2_put_super+0x300/0x860 fs/gfs2/super.c:618
generic_shutdown_super+0x13d/0x2d0 fs/super.c:647
kill_block_super+0x44/0x90 fs/super.c:1665
deactivate_locked_super+0xbc/0x130 fs/super.c:477
cleanup_mnt+0x3d3/0x460 fs/namespace.c:1317
task_work_run+0x1d9/0x270 kernel/task_work.c:233
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x73a/0x2360 kernel/exit.c:1004
do_group_exit+0x22d/0x2f0 kernel/exit.c:1147
__do_sys_exit_group kernel/exit.c:1158 [inline]
__se_sys_exit_group kernel/exit.c:1156 [inline]
__x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1156
x64_sys_call+0x221a/0x2240 arch/x86/include/generated/asm/syscalls_64.h:232
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8b89f9ce59
Code: Unable to access opcode bytes at 0x7f8b89f9ce2f.
RSP: 002b:00007ffc5b7df378 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 00007f8b8a03233c RCX: 00007f8b89f9ce59
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000001
RBP: 0000000000000016 R08: 0000000000000000 R09: 00007f8b8a0322ca
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffc5b7e0630
R13: 00007f8b8a0322ca R14: 0000555582f544e8 R15: 00007ffc5b7e49d0
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:_find_first_zero_bit+0x29/0xb0 lib/find_bit.c:149
Code: 90 f3 0f 1e fa 41 57 41 56 41 55 41 54 53 48 85 f6 74 46 48 89 f3 49 89 fe 49 bf 00 00 00 00 00 fc ff df 48 89 f8 48 c1 e8 03 <42> 80 3c 38 00 74 08 4c 89 f7 e8 b8 55 7c fd 49 8b 06 48 83 f8 ff
RSP: 0018:ffffc9000365f6c0 EFLAGS: 00010256
RAX: 0000000000000000 RBX: 000000000000f800 RCX: 0000000000000000
RDX: ffff888034374c40 RSI: 000000000000f800 RDI: 0000000000000000
RBP: dffffc0000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520006cbecc R12: ffff888058d1d3f0
R13: ffff888034374c38 R14: 0000000000000000 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff888125223000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8b8a06ea00 CR3: 000000000e746000 CR4: 0000000000350ef0
----------------
Code disassembly (best guess):
0: 90 nop
1: f3 0f 1e fa endbr64
5: 41 57 push %r15
7: 41 56 push %r14
9: 41 55 push %r13
b: 41 54 push %r12
d: 53 push %rbx
e: 48 85 f6 test %rsi,%rsi
11: 74 46 je 0x59
13: 48 89 f3 mov %rsi,%rbx
16: 49 89 fe mov %rdi,%r14
19: 49 bf 00 00 00 00 00 movabs $0xdffffc0000000000,%r15
20: fc ff df
23: 48 89 f8 mov %rdi,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1) <-- trapping instruction
2f: 74 08 je 0x39
31: 4c 89 f7 mov %r14,%rdi
34: e8 b8 55 7c fd call 0xfd7c55f1
39: 49 8b 06 mov (%r14),%rax
3c: 48 83 f8 ff cmp $0xffffffffffffffff,%rax


---
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[syzbot]

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***

Subject: [PATCH] gfs2: fix null-ptr-deref in gfs2_quota_hold during unmount
Author: karti...@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


gfs2_quota_cleanup() frees sd_quota_bitmap early in gfs2_put_super()
before the iput() calls that can trigger inode eviction. When an unlinked
inode is evicted during unmount, it goes through:

gfs2_evict_inode() -> gfs2_dinode_dealloc() -> gfs2_quota_hold()
-> qdsb_get() -> slot_get() -> find_first_zero_bit(sd_quota_bitmap)

If sd_quota_bitmap has already been freed by gfs2_quota_cleanup(), this
results in a null pointer dereference:

KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]

_find_first_zero_bit+0x29/0xb0 lib/find_bit.c:149
slot_get fs/gfs2/quota.c:355

qdsb_get+0x133/0x340 fs/gfs2/quota.c:522
gfs2_quota_hold+0x191/0x5c0 fs/gfs2/quota.c:606
gfs2_dinode_dealloc+0x176/0x3f0 fs/gfs2/inode.c:488

gfs2_evict_inode+0x11cd/0x1400 fs/gfs2/super.c:1479
gfs2_put_super+0x300/0x860 fs/gfs2/super.c:618

The same problem exists in both paths through gfs2_put_super(): the
direct gfs2_quota_cleanup() call in the read-only branch, and indirectly
via gfs2_make_fs_ro() in the read-write branch.

Fix this by removing gfs2_quota_cleanup() from gfs2_make_fs_ro() and
moving it to after all the iput() calls in gfs2_put_super(), ensuring
sd_quota_bitmap remains valid for the entire duration of inode eviction.
Restore an explicit gfs2_quota_cleanup() call in gfs2_reconfigure() after
gfs2_make_fs_ro() to preserve the remount-ro cleanup behaviour.

Reported-by: syzbot+cb79de...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=cb79de2cc8b76fbf474f
Signed-off-by: Deepanshu Kartikey <karti...@gmail.com>
---
fs/gfs2/ops_fstype.c | 1 +
fs/gfs2/super.c | 5 ++---
2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index 9b9e70f14d25..56bc966531f2 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -1592,6 +1592,7 @@ static int gfs2_reconfigure(struct fs_context *fc)
if ((sb->s_flags ^ fc->sb_flags) & SB_RDONLY) {
if (fc->sb_flags & SB_RDONLY) {
gfs2_make_fs_ro(sdp);
+ gfs2_quota_cleanup(sdp);
} else {
error = gfs2_make_fs_rw(sdp);
if (error)
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 4d854556b529..e13c9f9efe6c 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -565,7 +565,6 @@ void gfs2_make_fs_ro(struct gfs2_sbd *sdp)
HZ * 5);
gfs2_assert_warn(sdp, gfs2_log_is_empty(sdp));
}
- gfs2_quota_cleanup(sdp);
}

/**
@@ -604,8 +603,6 @@ static void gfs2_put_super(struct super_block *sb)
else {
if (gfs2_withdrawn(sdp))
gfs2_destroy_threads(sdp);
-
- gfs2_quota_cleanup(sdp);
}

/* At this point, we're through modifying the disk */
@@ -637,6 +634,8 @@ static void gfs2_put_super(struct super_block *sb)
gfs2_glock_dq_uninit(&sdp->sd_live_gh);
gfs2_clear_rgrpd(sdp);
gfs2_jindex_free(sdp);
+
+ gfs2_quota_cleanup(sdp);
/* Take apart glock structures and buffer lists */
gfs2_gl_hash_clear(sdp);
iput(sdp->sd_inode);
--
2.43.0

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
lost connection to test machine



Tested on:

commit: dc59e4fe Linux 7.2-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11dd8a89580000

kernel config: https://syzkaller.appspot.com/x/.config?x=86ba763b42fa66a
dashboard link: https://syzkaller.appspot.com/bug?extid=cb79de2cc8b76fbf474f
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=10b9f4ea580000