[PATCH] jfs: fix null log dereference from sb during readonly mode

[rafad900]

    #syz test

    Clearing the inode pointer is necessary to ensure no memory leaks
    after txBegin fails to initialize the superblock during read only
    mode.
    - This error was found by syzkaller
    - After ialloc() is called within jfs_create(), the inode pointer
    is created but never freed when txBegin() fails.
    - The patch addresses the need to stop commiting a file 
    transaction after txBegin() fails and the clean up of pointers. 
    - The patch was tested on QEMU with the repro provided by syzbot

Signed-off-by: rafad900 <19312533+rafad900@xxxxxxxxxxxxxxxxxxxxxxxx>
---
 fs/jfs/namei.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/jfs/namei.c b/fs/jfs/namei.c
index 60c4a0e0fca5..3a5f45cdeae0 100644
--- a/fs/jfs/namei.c
+++ b/fs/jfs/namei.c
@@ -97,7 +97,13 @@ 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");
+		free_ea_wmap(ip);
+		clear_nlink(ip);
+		discard_new_inode(ip);
+		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