jbd2: Avoid printing outside the boundary of the buffer

Theoretically possible that "%pg" will take all room for the j_devname
and hence the "-%lu" will go outside 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".

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230605170553.7835-2-andriy.shevchenko@linux.intel.com

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 8ae4191..6e17f8f 100644 (file)
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1491,7 +1491,6 @@ journal_t *jbd2_journal_init_inode(struct inode *inode)
 {
        journal_t *journal;
        sector_t blocknr;
-       char *p;
        int err = 0;
 
        blocknr = 0;
@@ -1515,9 +1514,8 @@ 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;