linux-kernel - Re: [PATCH] cifs: check kzalloc return

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Date:   Wed, 19 Dec 2018 08:22:50 +0100
From:   Nicholas Mc Guire <der.herr@...r.at>
To:     Joe Perches <joe@...ches.com>
Cc:     Nicholas Mc Guire <hofrat@...dl.org>,
        Steve French <sfrench@...ba.org>, linux-cifs@...r.kernel.org,
        samba-technical@...ts.samba.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cifs: check kzalloc return

On Tue, Dec 18, 2018 at 09:33:58AM -0800, Joe Perches wrote:
> On Tue, 2018-12-18 at 17:27 +0100, Nicholas Mc Guire wrote:
> > kzalloc can return NULL so a check is needed. While there is a
> > check for ret_buf there is no check for the allocation of
> > ret_buf->crfid.fid - this check is thus added. Both call-sites
> > of tconInfoAlloc() check for NULL return of tconInfoAlloc()
> > so returning NULL on failure of kzalloc() here seems appropriate.
> > As the kzalloc() is the only thing here that can fail it is
> > moved to the beginning so as not to initialize other resources
> > on failure of kzalloc.
> > 
> > Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> > Fixes: 3d4ef9a15343 ("smb3: fix redundant opens on root")
> > ---
> > 
> > Problem located with an experimental coccinelle script
> > 
> > While at it make checkpatch happy by using *ret_buf->crfid.fid
> > rather than struct cifs_fid.
> > 
> > Patch was compile tested with: x86_64_defconfig + CIFS=m
> > (with some unrelated smatch warnings and some pending cocci fixes)
> > 
> > Patch is against v4.20-rc7 (localversion-next is next-20181218)
> []
> > diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
> []
> > @@ -113,6 +113,13 @@ tconInfoAlloc(void)
> >  	struct cifs_tcon *ret_buf;
> >  	ret_buf = kzalloc(sizeof(struct cifs_tcon), GFP_KERNEL);
> >  	if (ret_buf) {
> > +		ret_buf->crfid.fid = kzalloc(sizeof(*ret_buf->crfid.fid),
> > +					     GFP_KERNEL);
> > +		if (!ret_buf->crfid.fid) {
> > +			kfree(ret_buf);
> > +			return NULL;
> > +		}
> > +
> >  		atomic_inc(&tconInfoAllocCount);
> >  		ret_buf->tidStatus = CifsNew;
> >  		++ret_buf->tc_count;
> > @@ -120,8 +127,6 @@ tconInfoAlloc(void)
> >  		INIT_LIST_HEAD(&ret_buf->tcon_list);
> >  		spin_lock_init(&ret_buf->open_file_lock);
> >  		mutex_init(&ret_buf->crfid.fid_mutex);
> > -		ret_buf->crfid.fid = kzalloc(sizeof(struct cifs_fid),
> > -					     GFP_KERNEL);
> >  		spin_lock_init(&ret_buf->stat_lock);
> >  		atomic_set(&ret_buf->num_local_opens, 0);
> >  		atomic_set(&ret_buf->num_remote_opens, 0);
> 
> Perhaps use a more common style by returning early on the
> first possible failure too so the block can be unindented.
>

yup the restructured cleanup would be the better way to go

rather than making this two patches I guess it would be the
best to just skip the intermediate kzalloc only cleanup -
atleast I see little value in that intermediat step - so
could you take care of the kzalloc() in your refactoring 
please ?

thx!
hofrat
 
> Maybe as a separate cleanup patch.
> ---
>  fs/cifs/misc.c | 34 ++++++++++++++++++++--------------
>  1 file changed, 20 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
> index 113980dba4d8..bee203055b30 100644
> --- a/fs/cifs/misc.c
> +++ b/fs/cifs/misc.c
> @@ -111,21 +111,27 @@ struct cifs_tcon *
>  tconInfoAlloc(void)
>  {
>  	struct cifs_tcon *ret_buf;
> -	ret_buf = kzalloc(sizeof(struct cifs_tcon), GFP_KERNEL);
> -	if (ret_buf) {
> -		atomic_inc(&tconInfoAllocCount);
> -		ret_buf->tidStatus = CifsNew;
> -		++ret_buf->tc_count;
> -		INIT_LIST_HEAD(&ret_buf->openFileList);
> -		INIT_LIST_HEAD(&ret_buf->tcon_list);
> -		spin_lock_init(&ret_buf->open_file_lock);
> -		mutex_init(&ret_buf->crfid.fid_mutex);
> -		ret_buf->crfid.fid = kzalloc(sizeof(struct cifs_fid),
> -					     GFP_KERNEL);
> -		spin_lock_init(&ret_buf->stat_lock);
> -		atomic_set(&ret_buf->num_local_opens, 0);
> -		atomic_set(&ret_buf->num_remote_opens, 0);
> +
> +	ret_buf = kzalloc(sizeof(*ret_buf), GFP_KERNEL);
> +	if (!ret_buf)
> +		return NULL;
> +	ret_buf->crfid.fid = kzalloc(sizeof(*ret_buf->crfid.fid), GFP_KERNEL);
> +	if (!ret_buf->crfid.fid) {
> +		kfree(ret_buf);
> +		return NULL;
>  	}
> +
> +	atomic_inc(&tconInfoAllocCount);
> +	ret_buf->tidStatus = CifsNew;
> +	++ret_buf->tc_count;
> +	INIT_LIST_HEAD(&ret_buf->openFileList);
> +	INIT_LIST_HEAD(&ret_buf->tcon_list);
> +	spin_lock_init(&ret_buf->open_file_lock);
> +	mutex_init(&ret_buf->crfid.fid_mutex);
> +	spin_lock_init(&ret_buf->stat_lock);
> +	atomic_set(&ret_buf->num_local_opens, 0);
> +	atomic_set(&ret_buf->num_remote_opens, 0);
> +
>  	return ret_buf;
>  }
>  
>