Re: [patch]check NULL pointer

Lukas Czerner
2011-06-10T08:32:41Z

On Fri, 10 Jun 2011, Shaohua Li wrote:

> On Thu, 2011-06-09 at 22:51 +0800, Eric Sandeen wrote:
> > On 6/9/11 4:24 AM, Lukas Czerner wrote:
> > > On Thu, 9 Jun 2011, Shaohua Li wrote:
> > >
> > >> orig_data could be NULL.
> > >
> > > Now, that is the commit description :). Could you please be more
> > > descriptive in the "descritpion" ? Also the subject is not right either,
> > > please see Documentation/SubmittingPatches
> >
> > Yes; if possible please use the commit message to describe how/why orig_data
> > can be NULL; a testcase if one exists; the resulting flaw (null pointer deref?)
> > etc.
> >
> > something like:
> >
> > Subject: [PATCH] ext4: check for NULL orig_data pointer in mount paths
> >
> > The orig_data pointer in ext4_fill_super() and ext4_remount()
> > can be null if < ??? >, which can lead to < ??? > in the mount
> > and remount paths. This can be demonstrated by < ??? >.
> > To avoid this, we can simply test for the null pointer
> > and return an error in ext4_fill_super() and ext4_remount().
> I thought the reason is pretty straightforward, anyway here is the
> updated patch.
>
> Subject: [patch]ext4: check NULL pointer for mount and remount
>
> orig_data could be NULL, because the memory allocation of kstrdup() could fail.
> Add the NULL check.

I am sorry, but as I pointed out in previous mail this is not true.
*orig_data can be also NULL in the case that *data is NULL and hence
there is no reason for exiting with error. Also please use the subject
Eric suggested.

Thanks!
-Lukas

>
> Signed-off-by: Shaohua Li <shaohua.li@intel.com>
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index cc5c157..45fc255 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3057,6 +3057,8 @@ 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;
>
> + if (!orig_data)
> + return ret;
> sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> if (!sbi)
> goto out_free_orig;
> @@ -4285,6 +4287,8 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
> #endif
> char *orig_data = kstrdup(data, GFP_KERNEL);
>
> + if (!orig_data)
> + return -ENOMEM;
> /* Store the original options */
> lock_super(sb);
> old_sb_flags = sb->s_flags;
>
>
>

--