[syzbot] [jfs?] [fat?] general protection fault in txEnd

[Rafael Alejandro Diaz Cruz <rafad900@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 10 bytes --]

#syz test

[-- Attachment #2: 0001-jfs-prevent-null-log-deference-from-superblock-durin.patch --]
[-- Type: text/x-diff, Size: 1310 bytes --]

From b530db0e1844ca2b8fecf527dd5d5457e329adf0 Mon Sep 17 00:00:00 2001
From: rafad900 <19312533+rafad900@users.noreply.github.com>
Date: Fri, 27 Mar 2026 18:58:45 -0700
Subject: [PATCH] jfs: prevent null log deference from superblock during read
 only mode

Its not possible to use jfs_create() while the file system is in read
only mode. However, there is not a way for jfs_create() to handle this case
when txBegin fails. So jfs_create() continues to with the changes to the
filesystem and tries to txCommit() them, but when trying to write the changes
to the ->log of the superblock, we reach an error telling us that system
cannot write and enters panic.

Signed-off-by: rafad900 <19312533+rafad900@users.noreply.github.com>
---
 fs/jfs/namei.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/jfs/namei.c b/fs/jfs/namei.c
index 60c4a0e0fca5..25b303276b82 100644
--- a/fs/jfs/namei.c
+++ b/fs/jfs/namei.c
@@ -97,6 +97,10 @@ static int jfs_create(struct mnt_idmap *idmap, struct inode *dip,
 	}
 
 	tid = txBegin(dip->i_sb, 0);
+	if (tid == 0) {
+		jfs_err("jfs_create: unable to create tblk due to read only filesystem");
+		return -EROFS;
+	}
 
 	mutex_lock_nested(&JFS_IP(dip)->commit_mutex, COMMIT_MUTEX_PARENT);
 	mutex_lock_nested(&JFS_IP(ip)->commit_mutex, COMMIT_MUTEX_CHILD);
-- 
2.43.0