linux-ext4 - [PATCH AUTOSEL 6.1 06/13] ext4: update s_journal

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Date:   Tue, 14 Mar 2023 08:43:18 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Baokun Li <libaokun1@...wei.com>,
        Luís Henriques <lhenriques@...e.de>,
        Jan Kara <jack@...e.cz>, Theodore Ts'o <tytso@....edu>,
        Sasha Levin <sashal@...nel.org>, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org
Subject: [PATCH AUTOSEL 6.1 06/13] ext4: update s_journal_inum if it changes after journal replay

From: Baokun Li <libaokun1@...wei.com>

[ Upstream commit 3039d8b8692408438a618fac2776b629852663c3 ]

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>
Reviewed-by: Jan Kara <jack@...e.cz>
Link: https://lore.kernel.org/r/20230107032126.4165860-3-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 8011600999586..2528e8216c334 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5967,8 +5967,11 @@ 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);
 	}
 
-- 
2.39.2