[syzbot] [gfs2?] WARNING in gfs2_check_blk_type (2)

[syzbot] [gfs2?] WARNING in gfs2_check_blk_type (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    90d35da658da Linux 6.8-rc7
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=10bb48e4180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=119d08814b43915b
dashboard link: https://syzkaller.appspot.com/bug?extid=26e96d7e92eed8a21405
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17fcb02e180000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1028a27a180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/821deeb51f0a/disk-90d35da6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9a7d492f89d7/vmlinux-90d35da6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/78bfac3e2f5d/bzImage-90d35da6.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/a2629006a328/mount_0.gz

Bisection is inconclusive: the issue happens on the oldest tested release.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=130748e4180000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=108748e4180000
console output: https://syzkaller.appspot.com/x/log.txt?x=170748e4180000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+26e96d7e92eed8a21405@syzkaller.appspotmail.com

gfs2: fsid=syz:syz.0: first mount done, others may mount
------------[ cut here ]------------
WARNING: CPU: 1 PID: 5058 at fs/gfs2/rgrp.c:2630 gfs2_check_blk_type+0x44e/0x680 fs/gfs2/rgrp.c:2630
Modules linked in:
CPU: 1 PID: 5058 Comm: syz-executor354 Not tainted 6.8.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
RIP: 0010:gfs2_check_blk_type+0x44e/0x680 fs/gfs2/rgrp.c:2630
Code: d4 01 00 00 8b 1b 89 df 44 89 f6 e8 4c 49 bd fd 4c 89 74 24 10 44 39 f3 76 23 e8 7d 47 bd fd 45 31 ed eb 70 e8 73 47 bd fd 90 <0f> 0b 90 41 bf f9 ff ff ff 48 8b 5c 24 18 e9 46 01 00 00 e8 5a 47
RSP: 0018:ffffc900040d78c0 EFLAGS: 00010293
RAX: ffffffff83d6242c RBX: ffff88802ee40028 RCX: ffff8880779e0000
RDX: 0000000000000000 RSI: 0000000000000012 RDI: 0000000000000013
RBP: ffffc900040d79d0 R08: ffffffff83d62422 R09: 1ffff1100f3b75dc
R10: dffffc0000000000 R11: ffffed100f3b75dd R12: 1ffff11005dc8006
R13: ffff88802ee40000 R14: 0000000000000012 R15: 0000000000000013
FS:  000055555631c380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000066c7e0 CR3: 000000002aba0000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 gfs2_inode_lookup+0xb05/0xc60 fs/gfs2/inode.c:178
 gfs2_lookup_by_inum+0x51/0xf0 fs/gfs2/inode.c:251
 gfs2_get_dentry fs/gfs2/export.c:139 [inline]
 gfs2_fh_to_dentry+0x13a/0x1f0 fs/gfs2/export.c:160
 exportfs_decode_fh_raw+0x152/0x5f0 fs/exportfs/expfs.c:444
 exportfs_decode_fh+0x3c/0x80 fs/exportfs/expfs.c:584
 do_handle_to_path fs/fhandle.c:155 [inline]
 handle_to_path fs/fhandle.c:210 [inline]
 do_handle_open+0x494/0x650 fs/fhandle.c:226
 do_syscall_64+0xf9/0x240
 entry_SYSCALL_64_after_hwframe+0x6f/0x77
RIP: 0033:0x7f87a993d839
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 61 17 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:00007fff387ac1f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000130
RAX: ffffffffffffffda RBX: 00007fff387ac3c8 RCX: 00007f87a993d839
RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000000000004
RBP: 00007f87a99c3610 R08: 0000000000000000 R09: 00007fff387ac3c8
R10: 00007f87a9978bf3 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fff387ac3b8 R14: 0000000000000001 R15: 0000000000000001
 </TASK>


---
This report is generated by a bot. It may contain errors.
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syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Forwarded: [PATCH] gfs2: remove WARN_ON_ONCE in gfs2_check_blk_type

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: [PATCH] gfs2: remove WARN_ON_ONCE in gfs2_check_blk_type
Author: tristmd@gmail.com

From: Tristan Madani <tristan@talencesecurity.com>

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


gfs2_check_blk_type() calls gfs2_rbm_from_block() and wraps the error
check in WARN_ON_ONCE():

    error = gfs2_rbm_from_block(&rbm, no_addr);
    if (!WARN_ON_ONCE(error)) {

When the block address falls outside the resource group (which happens
with corrupted on-disk metadata), gfs2_rbm_from_block() returns an
error and the WARN_ON_ONCE fires, producing a kernel stack trace.

The error is already handled correctly by the function -- the block
type test is skipped and the error code propagates to the caller.
Only the WARNING itself is problematic.

Replace the WARN_ON_ONCE with a plain error check and map the error
to -ESTALE for the caller (gfs2_fh_to_dentry).

Reported-by: syzbot+26e96d7e92eed8a21405@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=26e96d7e92eed8a21405
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
 fs/gfs2/rgrp.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
index XXXXXXX..XXXXXXX 100644
--- a/fs/gfs2/rgrp.c
+++ b/fs/gfs2/rgrp.c
@@ -2627,7 +2627,10 @@ int gfs2_check_blk_type(struct gfs2_sbd *sdp, u64 no_addr, unsigned int type)

 	rbm.rgd = rgd;
 	error = gfs2_rbm_from_block(&rbm, no_addr);
-	if (!WARN_ON_ONCE(error)) {
+	if (error) {
+		error = -ESTALE;
+	} else {
 		/*
 		 * No need to take the local resource group lock here; the
 		 * inode glock of @no_addr provides the necessary
--
2.43.0

Forwarded: Re: [syzbot] WARNING in gfs2_check_blk_type

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Re: [syzbot] WARNING in gfs2_check_blk_type
Author: tristmd@gmail.com

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>From a57e64056f6b6fa2ede96b624b49baeb5269478b Mon Sep 17 00:00:00 2001
From: Tristan Madani <tristan@talencesecurity.com>
Date: Fri, 17 Apr 2026 16:15:20 +0000
Subject: [PATCH] gfs2: remove WARN_ON_ONCE in gfs2_check_blk_type()
gfs2_check_blk_type() wraps gfs2_rbm_from_block() in
!WARN_ON_ONCE(), triggering a kernel WARNING on corrupted
filesystems. Replace with a plain error check and map the
error to -ESTALE for the caller.
Reported-by: syzbot+26e96d7e92eed8a21405@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=26e96d7e92eed8a21405
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
 fs/gfs2/rgrp.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
index 5988a16..da94c25 100644
--- a/fs/gfs2/rgrp.c
+++ b/fs/gfs2/rgrp.c
@@ -2625,7 +2625,9 @@ int gfs2_check_blk_type(struct gfs2_sbd *sdp, u64 no_addr, unsigned int type)
 
 	rbm.rgd = rgd;
 	error = gfs2_rbm_from_block(&rbm, no_addr);
-	if (!WARN_ON_ONCE(error)) {
+	if (error) {
+		error = -ESTALE;
+	} else {
 		/*
 		 * No need to take the local resource group lock here; the
 		 * inode glock of @no_addr provides the necessary
-- 
2.47.3