On Nov 17, 2016, at 9:26 PM, Theodore Ts'o <tytso@xxxxxxx> wrote:
>
> Fix a large number of problems with how we handle mount options in the
> superblock. For one, if the string in the superblock is long enough
> that it is not null terminated, we could run off the end of the string
> and try to interpret superblocks fields as characters. It's unlikely
> this will cause a security problem, but it could result in an invalid
> parse. Also, parse_options is destructive to the string, so in some
> cases if there is a comma-separated string, it would be modified in
> the superblock. (Fortunately it only happens on file systems with a
> 1k block size.)
>
> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> fs/ext4/super.c | 37 ++++++++++++++++++++++---------------
> 1 file changed, 22 insertions(+), 15 deletions(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 12f50ef56fe1..3009c03220d6 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3303,7 +3303,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> char *orig_data = kstrdup(data, GFP_KERNEL);
> struct buffer_head *bh;
> struct ext4_super_block *es = NULL;
> - struct ext4_sb_info *sbi;
> + struct ext4_sb_info *sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> ext4_fsblk_t block;
> ext4_fsblk_t sb_block = get_sb_block(&data);
> ext4_fsblk_t logical_sb_block;
> @@ -3321,17 +3321,17 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> int err = 0;
> unsigned int journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
> ext4_group_t first_not_zeroed;
> + char *s_mount_opts = kzalloc(sizeof(sbi->s_es->s_mount_opts)+1,
> + GFP_KERNEL);
This doesn't check if "sbi" is non-NULL before dereferencing it. While
there isn't really any likelihood for this allocation to fail, I don't
think there is any benefit to moving these allocations to the declaration.
> - sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> - if (!sbi)
> - goto out_free_orig;
> + if ((data && !orig_data) || !s_mount_opts || !sbi)
> + goto out_free_base;
>
> sbi->s_blockgroup_lock =
> kzalloc(sizeof(struct blockgroup_lock), GFP_KERNEL);
> - if (!sbi->s_blockgroup_lock) {
> - kfree(sbi);
> - goto out_free_orig;
> - }
> + if (!sbi->s_blockgroup_lock)
> + goto out_free_base;
> +
> sb->s_fs_info = sbi;
> sbi->s_sb = sb;
> sbi->s_inode_readahead_blks = EXT4_DEF_INODE_READAHEAD_BLKS;
> @@ -3477,11 +3477,15 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> */
> sbi->s_li_wait_mult = EXT4_DEF_LI_WAIT_MULT;
>
> - if (!parse_options((char *) sbi->s_es->s_mount_opts, sb,
> - &journal_devnum, &journal_ioprio, 0)) {
> - ext4_msg(sb, KERN_WARNING,
> - "failed to parse options in superblock: %s",
> - sbi->s_es->s_mount_opts);
> + if (sbi->s_es->s_mount_opts[0]) {
> + strncpy(s_mount_opts, sbi->s_es->s_mount_opts,
> + sizeof(sbi->s_es->s_mount_opts));
This could use kstrndup()? It always allocates an extra byte for the NUL.
> + 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);
> + }
> }
> sbi->s_def_mount_opt = sbi->s_mount_opt;
> if (!parse_options((char *) data, sb, &journal_devnum,
> @@ -4162,7 +4166,9 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>
> if (___ratelimit(&ext4_mount_msg_ratelimit, "EXT4-fs mount"))
> ext4_msg(sb, KERN_INFO, "mounted filesystem with%s. "
> - "Opts: %s%s%s", descr, sbi->s_es->s_mount_opts,
> + "Opts: %.*s%s%s", descr,
> + sizeof(sbi->s_es->s_mount_opts),
> + sbi->s_es->s_mount_opts,
This isn't really needed, since there is always a NUL terminator added
to the string?
> *sbi->s_es->s_mount_opts ? "; " : "", orig_data);
>
> if (es->s_error_count)
> @@ -4241,9 +4247,10 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> out_fail:
> sb->s_fs_info = NULL;
> kfree(sbi->s_blockgroup_lock);
> +out_free_base:
> kfree(sbi);
> -out_free_orig:
> kfree(orig_data);
> + kfree(s_mount_opts);
> return err ? err : ret;
> }
Cheers, Andreas
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