[PATCH] FS: JFS: Check for read-only mounted filesystem in txBegin

[mirimmad]

From: Immad Mir <mirimmad17@xxxxxxxxx>

 This patch adds a check for read-only mounted filesystem
 in txBegin before starting a transaction potentially saving
 from NULL pointer deref.

Signed-off-by: Immad Mir <mirimmad17@xxxxxxxxx>
---
 fs/jfs/jfs_txnmgr.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/jfs/jfs_txnmgr.c b/fs/jfs/jfs_txnmgr.c
index ffd4feece..87dc4e3a4 100644
--- a/fs/jfs/jfs_txnmgr.c
+++ b/fs/jfs/jfs_txnmgr.c
@@ -353,7 +353,10 @@ tid_t txBegin(struct super_block *sb, int flag)
 
 	jfs_info("txBegin: flag = 0x%x", flag);
 	log = JFS_SBI(sb)->log;
-
+	if (!log) {
+		jfs_error(sb, "read-only filesystem\n");
+		return 0;
+	}
 	TXN_LOCK();
 
 	INCREMENT(TxStat.txBegin);
-- 
2.40.0