linux-ext4 - [PATCH 2/2] ext4: update s_journal_inum if it changes after journal replay

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Date:   Fri, 6 Jan 2023 18:47:06 +0800
From:   Baokun Li <libaokun1@...wei.com>
To:     <linux-ext4@...r.kernel.org>
CC:     <tytso@....edu>, <adilger.kernel@...ger.ca>, <jack@...e.cz>,
        <ritesh.list@...il.com>, <linux-kernel@...r.kernel.org>,
        <yi.zhang@...wei.com>, <yukuai3@...wei.com>,
        <libaokun1@...wei.com>,
        Luís Henriques <lhenriques@...e.de>
Subject: [PATCH 2/2] ext4: update s_journal_inum if it changes after journal replay

When mounting a crafted ext4 image, s_journal_inum may change after journal
replay, which is obviously unreasonable because we have successfully loaded
and replayed the journal through the old s_journal_inum. And the new
s_journal_inum bypasses some of the checks in ext4_get_journal(), which
may trigger a null pointer dereference problem. So if s_journal_inum
changes after the journal replay, we ignore the change, and rewrite the
current journal_inum to the superblock.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216541
Reported-by: Luís Henriques <lhenriques@...e.de>
Signed-off-by: Baokun Li <libaokun1@...wei.com>
---
 fs/ext4/super.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 260c1b3e3ef2..3fe9dc19ff9c 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5953,8 +5953,11 @@ static int ext4_load_journal(struct super_block *sb,
 	if (!really_read_only && journal_devnum &&
 	    journal_devnum != le32_to_cpu(es->s_journal_dev)) {
 		es->s_journal_dev = cpu_to_le32(journal_devnum);
-
-		/* Make sure we flush the recovery flag to disk. */
+		ext4_commit_super(sb);
+	}
+	if (!really_read_only && journal_inum &&
+	    journal_inum != le32_to_cpu(es->s_journal_inum)) {
+		es->s_journal_inum = cpu_to_le32(journal_inum);
 		ext4_commit_super(sb);
 	}
 
-- 
2.31.1