Re: [patch]check NULL pointer

Shaohua Li
2011-06-10T06:34:55Z

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.

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;