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SubjectRe: [PATCH] ext4: fix NULL pointer dereference from orig_data in fill_super and remount.
On 11/06/2011 08:49 PM, Namjae Jeon wrote:
> Fix NULL pointer dereference from orig_data in fill_super and remount.
>
> Signed-off-by: Namjae Jeon <linkinjeon@gmail.com>
> ---
> fs/ext4/super.c | 12 ++++++++++--
> 1 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 9953d80..3770d3f 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3102,7 +3102,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> __releases(kernel_lock)
> __acquires(kernel_lock)
> {
> - char *orig_data = kstrdup(data, GFP_KERNEL);
> struct buffer_head *bh;
> struct ext4_super_block *es = NULL;
> struct ext4_sb_info *sbi;
> @@ -3124,6 +3123,10 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> int err;
> unsigned int journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
> ext4_group_t first_not_zeroed;
> +
> + char *orig_data = kstrdup(data, GFP_KERNEL);
> + if (!orig_data)
> + return ret;
>
> sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> if (!sbi)
> @@ -4398,6 +4401,10 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
> int i;
> #endif
> char *orig_data = kstrdup(data, GFP_KERNEL);
> + if (!orig_data) {
> + err = -ENOMEM;
> + goto failed_alloc_orig;

I didn't quite get why 'failed_alloc_orig' is needed here.
Why can't we just return -ENOMEM? Anyway we haven't yet
clobbered any opts at this point, right?

See my comments below.

> + }
>
> /* Store the original options */
> lock_super(sb);
> @@ -4562,6 +4569,8 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
> return 0;
>
> restore_opts:
> + kfree(orig_data);
> +failed_alloc_orig:
> sb->s_flags = old_sb_flags;
> sbi->s_mount_opt = old_opts.s_mount_opt;
> sbi->s_mount_opt2 = old_opts.s_mount_opt2;

This would put garbage values in sb->... and sbi->... when we jump
to 'failed_alloc_orig' upon 'orig_data' allocation failure, because
the old_* variables were still uninitialized at that point.

> @@ -4580,7 +4589,6 @@ restore_opts:
> }
> #endif
> unlock_super(sb);
> - kfree(orig_data);
> return err;
> }
>

Thanks,
Srivatsa S. Bhat


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