linux-kernel - Re: [PATCH][next] pstore/zone,blk: fix dereference of pointer before it has been null checked

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Message-ID: <202005121158.4D49A98839@keescook>
Date:   Tue, 12 May 2020 11:58:23 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Colin King <colin.king@...onical.com>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        WeiXiong Liao <liaoweixiong@...winnertech.com>,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] pstore/zone,blk: fix dereference of pointer before
 it has been null checked

On Tue, May 12, 2020 at 06:07:19PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently the assignment of ctx dereferences pointer 'record' before
> the pointer has been null checked. Fix this by only making this
> dereference after it has been null checked close to the point ctx
> is to be used.
> 
> Addresses-Coverity: ("Dereference before null check")
> Fixes: bb4ccd1e6f56 ("pstore/zone,blk: Add ftrace frontend support")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

Thanks; applied.

-Kees

> ---
>  fs/pstore/zone.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/pstore/zone.c b/fs/pstore/zone.c
> index bd8e194110fc..c5bf3b9f644f 100644
> --- a/fs/pstore/zone.c
> +++ b/fs/pstore/zone.c
> @@ -998,7 +998,7 @@ static ssize_t psz_kmsg_read(struct pstore_zone *zone,
>  static ssize_t psz_ftrace_read(struct pstore_zone *zone,
>  		struct pstore_record *record)
>  {
> -	struct psz_context *cxt = record->psi->data;
> +	struct psz_context *cxt;
>  	struct psz_buffer *buf;
>  	int ret;
>  
> @@ -1018,6 +1018,7 @@ static ssize_t psz_ftrace_read(struct pstore_zone *zone,
>  		return ret;
>  
>  out:
> +	cxt = record->psi->data;
>  	if (cxt->ftrace_read_cnt < cxt->ftrace_max_cnt)
>  		/* then, read next ftrace zone */
>  		return -ENOMSG;
> -- 
> 2.25.1
> 

-- 
Kees Cook