[PATCH 6.1 061/183] [PATCH AUTOSEL 4.19 11/11] FS: JFS: Check for read-only mounted filesystem in txBegin

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

[ Upstream commit 95e2b352c03b0a86c5717ba1d24ea20969abcacc ]

 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>
Signed-off-by: Dave Kleikamp <dave.kleikamp@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/jfs/jfs_txnmgr.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/fs/jfs/jfs_txnmgr.c
+++ b/fs/jfs/jfs_txnmgr.c
@@ -354,6 +354,11 @@ tid_t txBegin(struct super_block *sb, in
 	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);