ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()

[ Upstream commit 8ecb790ea8c3fc69e77bace57f14cf0d7c177bd8 ]

Unlike other strings in the ext4 superblock, we rely on tune2fs to
make sure s_mount_opts is NUL terminated.  Harden
parse_apply_sb_mount_options() by treating s_mount_opts as a potential
__nonstring.

Cc: stable@vger.kernel.org
Fixes: 8b67f04ab9de ("ext4: Add mount options in superblock")
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Message-ID: <20250916-tune2fs-v2-1-d594dc7486f0@mit.edu>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[ applied to ext4_fill_super() instead of parse_apply_sb_mount_options() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 3957ff246bff29b2118a63b0218db556a8f52210..453e746ba361a27653bc6b52e85e576b849bc0d4 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4282,18 +4282,16 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
        }
 
        if (sbi->s_es->s_mount_opts[0]) {
-               char *s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
-                                             sizeof(sbi->s_es->s_mount_opts),
-                                             GFP_KERNEL);
-               if (!s_mount_opts)
-                       goto failed_mount;
+               char s_mount_opts[65];
+
+               strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts,
+                           sizeof(s_mount_opts));
                if (!parse_options(s_mount_opts, sb, &journal_devnum,
                                   &journal_ioprio, 0)) {
                        ext4_msg(sb, KERN_WARNING,
                                 "failed to parse options in superblock: %s",
                                 s_mount_opts);
                }
-               kfree(s_mount_opts);
        }
        sbi->s_def_mount_opt = sbi->s_mount_opt;
        if (!parse_options((char *) data, sb, &journal_devnum,