linux-kernel - [PATCH v1 1/3] jbd2: Avoid printing out the boundary

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Date:   Wed, 22 Mar 2023 16:12:04 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Cezary Rojewski <cezary.rojewski@...el.com>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     "Theodore Ts'o" <tytso@....edu>, Jan Kara <jack@...e.com>,
        Andy Shevchenko <andy@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: [PATCH v1 1/3] jbd2: Avoid printing out the boundary

Theoretically possible that "%pg" will take all room for the j_devname
and hence the "-%lu" will go out the boundary due to unconditional
sprintf() in use. To make this code more robust, replace two sequential
s*printf():s by a single call and then replace forbidden character.
It's possible to do this way, because '/' won't ever be in the result
of "-%lu".

Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
 fs/jbd2/journal.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 8ae419152ff6..00c0aa4a3a91 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1515,9 +1515,8 @@ journal_t *jbd2_journal_init_inode(struct inode *inode)
 
 	journal->j_inode = inode;
 	snprintf(journal->j_devname, sizeof(journal->j_devname),
-		 "%pg", journal->j_dev);
-	p = strreplace(journal->j_devname, '/', '!');
-	sprintf(p, "-%lu", journal->j_inode->i_ino);
+		 "%pg-%lu", journal->j_dev, journal->j_inode->i_ino);
+	strreplace(journal->j_devname, '/', '!');
 	jbd2_stats_proc_init(journal);
 
 	return journal;
-- 
2.40.0.1.gaa8946217a0b