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

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>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d26e5c0731e5e3706ffe93a364bfb6ba44c3bf59..488f4c281a3f4b1442430d48680b1bcb0286a03b 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2469,7 +2469,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
                                        struct ext4_fs_context *m_ctx)
 {
        struct ext4_sb_info *sbi = EXT4_SB(sb);
-       char *s_mount_opts = NULL;
+       char s_mount_opts[65];
        struct ext4_fs_context *s_ctx = NULL;
        struct fs_context *fc = NULL;
        int ret = -ENOMEM;
@@ -2477,15 +2477,11 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
        if (!sbi->s_es->s_mount_opts[0])
                return 0;
 
-       s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
-                               sizeof(sbi->s_es->s_mount_opts),
-                               GFP_KERNEL);
-       if (!s_mount_opts)
-               return ret;
+       strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts);
 
        fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
        if (!fc)
-               goto out_free;
+               return -ENOMEM;
 
        s_ctx = kzalloc(sizeof(struct ext4_fs_context), GFP_KERNEL);
        if (!s_ctx)
@@ -2517,11 +2513,8 @@ parse_failed:
        ret = 0;
 
 out_free:
-       if (fc) {
-               ext4_fc_free(fc);
-               kfree(fc);
-       }
-       kfree(s_mount_opts);
+       ext4_fc_free(fc);
+       kfree(fc);
        return ret;
 }