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

[syzbot <syzbot+cb79de2cc8b76fbf474f@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in _find_first_zero_bit

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: 6218 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026
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 68 06 7b fd 49 8b 06 48 83 f8 ff
RSP: 0018:ffffc90002ec76c0 EFLAGS: 00010256
RAX: 0000000000000000 RBX: 000000000000f800 RCX: 0000000000000000
RDX: ffff88802888cc40 RSI: 000000000000f800 RDI: 0000000000000000
RBP: dffffc0000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520005d8ecc R12: ffff88805dd283f0
R13: ffff88802888cc38 R14: 0000000000000000 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888125207000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000013ecc44fd000 CR3: 000000000e746000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 find_first_zero_bit include/linux/find.h:391 [inline]
 slot_get fs/gfs2/quota.c:369 [inline]
 qdsb_get+0x133/0x340 fs/gfs2/quota.c:536
 gfs2_quota_hold+0x191/0x5c0 fs/gfs2/quota.c:620
 gfs2_dinode_dealloc+0x176/0x3f0 fs/gfs2/inode.c:529
 evict_unlinked_inode fs/gfs2/super.c:1334 [inline]
 gfs2_evict_inode+0x11e0/0x1410 fs/gfs2/super.c:1484
 evict+0x624/0xb50 fs/inode.c:822
 gfs2_put_super+0x300/0x870 fs/gfs2/super.c:620
 generic_shutdown_super+0x13d/0x2d0 fs/super.c:769
 kill_block_super+0x44/0xa0 fs/super.c:1918
 deactivate_locked_super+0xbc/0x110 fs/super.c:603
 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:1009
 do_group_exit+0x22d/0x2f0 kernel/exit.c:1152
 __do_sys_exit_group kernel/exit.c:1163 [inline]
 __se_sys_exit_group kernel/exit.c:1161 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1161
 x64_sys_call+0x2237/0x2250 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: 0033:0x7fe33439ce59
Code: Unable to access opcode bytes at 0x7fe33439ce2f.
RSP: 002b:00007ffe494bbc48 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 00007fe33443233c RCX: 00007fe33439ce59
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000001
RBP: 0000000000000016 R08: 0000000000000000 R09: 00007fe3344322ca
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffe494bcf00
R13: 00007fe3344322ca R14: 000055558ebba4e8 R15: 00007ffe494c12a0
 </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 68 06 7b fd 49 8b 06 48 83 f8 ff
RSP: 0018:ffffc90002ec76c0 EFLAGS: 00010256
RAX: 0000000000000000 RBX: 000000000000f800 RCX: 0000000000000000
RDX: ffff88802888cc40 RSI: 000000000000f800 RDI: 0000000000000000
RBP: dffffc0000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520005d8ecc R12: ffff88805dd283f0
R13: ffff88802888cc38 R14: 0000000000000000 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888125207000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000013ecc44fd000 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 68 06 7b fd       	call   0xfd7b06a1
  39:	49 8b 06             	mov    (%r14),%rax
  3c:	48 83 f8 ff          	cmp    $0xffffffffffffffff,%rax


Tested on:

commit:         8ea0df12 gfs2: Add meta inode validation to prevent co..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2.git
console output: https://syzkaller.appspot.com/x/log.txt?x=15ca0579580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f8dd02b32fb43dc7
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

Note: no patches were applied.