[ext4-next] ext4: fix null pointer dereference on sbi

From: Colin Ian King <colin.king@canonical.com>

In the case of a kzalloc failure when allocating sbi we end up
with a null pointer dereference on sbi when assigning sbi->s_daxdev.
Fix this by moving the assignment of sbi->s_daxdev to after the
null pointer check of sbi.

Detected by CoverityScan CID#1455379 ("Dereference before null check")

Fixes: 5e405595e5bf ("ext4: perform dax_device lookup at mount")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 fs/ext4/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On Tue, Sep 5, 2017 at 9:51 AM, Colin King <colin.king@canonical.com> wrote:
> From: Colin Ian King <colin.king@canonical.com>
>
> In the case of a kzalloc failure when allocating sbi we end up
> with a null pointer dereference on sbi when assigning sbi->s_daxdev.
> Fix this by moving the assignment of sbi->s_daxdev to after the
> null pointer check of sbi.
>
> Detected by CoverityScan CID#1455379 ("Dereference before null check")
>
> Fixes: 5e405595e5bf ("ext4: perform dax_device lookup at mount")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  fs/ext4/super.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 0e63fcd12c5b..71b9a667e1bc 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3422,10 +3422,10 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>         unsigned int journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
>         ext4_group_t first_not_zeroed;
>
> -       sbi->s_daxdev = dax_dev;
>         if ((data && !orig_data) || !sbi)
>                 goto out_free_base;
>
> +       sbi->s_daxdev = dax_dev;
>         sbi->s_blockgroup_lock =
>                 kzalloc(sizeof(struct blockgroup_lock), GFP_KERNEL);
>         if (!sbi->s_blockgroup_lock)

Thanks, this looks obviously correct to me. I'll append to the branch
with 5e405595e5bf.