Re: f2fs: avoid abnormal behavior on broken symlink

[Chao Yu <chao2.yu@samsung.com>]

Hi all,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@kernel.org]
> Sent: Wednesday, April 22, 2015 2:21 AM
> To: Dan Carpenter
> Cc: linux-f2fs-devel@lists.sourceforge.net
> Subject: Re: [f2fs-dev] f2fs: avoid abnormal behavior on broken symlink
> 
> Hi Dan,
> 
> Thank you for letting me know.
> I wrote a patch for this below.
> 
> Thanks,
> 
> On Mon, Apr 20, 2015 at 05:49:47PM +0300, Dan Carpenter wrote:
> > Hello Jaegeuk Kim,
> >
> > The patch feb7cbb079e6: "f2fs: avoid abnormal behavior on broken
> > symlink" from Apr 15, 2015, leads to the following static checker
> > warning:
> >
> > 	fs/f2fs/namei.c:304 f2fs_follow_link()
> > 	warn: 'page' isn't an ERR_PTR
> >
> > fs/f2fs/namei.c
> >    299  static void *f2fs_follow_link(struct dentry *dentry, struct nameidata *nd)
> >    300  {
> >    301          struct page *page;
> >    302
> >    303          page = page_follow_link_light(dentry, nd);
> >    304          if (IS_ERR(page))
> >                            ^^^^
> > The code in page_follow_link_light() is a bit hard to follow but it
> > returns NULL on error.

I try to find out the other callers' error handling method for
page_follow_link_light, and it shows all of them use the "IS_ERR" one.

In page_follow_link_light I also can't find a path which will return a NULL value.

So, Dan, is that report from smatch not true? or I made a mistake? If so, please
correct me.

Thanks,

> >
> >    305                  return page;
> >    306
> >    307          /* this is broken symlink case */
> >    308          if (*nd_get_link(nd) == 0) {
> >    309                  kunmap(page);
> >                         ^^^^^^^^^^^^
> > Potential NULL deref.
> >
> >    310                  page_cache_release(page);
> >    311                  return ERR_PTR(-ENOENT);
> >    312          }
> >    313          return page;
> >    314  }
> >
> > regards,
> > dan carpenter
> 
> >From 52889398489d4edc0cb016ae24036b994e3d9ccd Mon Sep 17 00:00:00 2001
> From: Jaegeuk Kim <jaegeuk@kernel.org>
> Date: Mon, 20 Apr 2015 16:30:14 -0700
> Subject: [PATCH] f2fs: fix wrong error hanlder in f2fs_follow_link
> 
> The page_follow_link_light returns NULL and its error pointer was remained
> in nd->path.
> 
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
>  fs/f2fs/namei.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> index 407dde3..678b6dd 100644
> --- a/fs/f2fs/namei.c
> +++ b/fs/f2fs/namei.c
> @@ -301,8 +301,8 @@ static void *f2fs_follow_link(struct dentry *dentry, struct nameidata *nd)
>  	struct page *page;
> 
>  	page = page_follow_link_light(dentry, nd);
> -	if (IS_ERR(page))
> -		return page;
> +	if (!page)
> +		return NULL;
> 
>  	/* this is broken symlink case */
>  	if (*nd_get_link(nd) == 0) {
> --
> 2.1.1
> 
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