From aa7cdf487ab3fa47284daaccc3d7d5de01c6a84c Mon Sep 17 00:00:00 2001
From: Immad Mir <mirimmad17@gmail.com>
Date: Fri, 23 Jun 2023 19:17:08 +0530
Subject: [PATCH] FS: JFS: Check for read-only mounted filesystem in txBegin

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

diff --git a/fs/jfs/jfs_txnmgr.c b/fs/jfs/jfs_txnmgr.c
index ffd4feece078..ce4b4760fcb1 100644
--- a/fs/jfs/jfs_txnmgr.c
+++ b/fs/jfs/jfs_txnmgr.c
@@ -354,6 +354,11 @@ 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);