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

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Date:   Tue, 12 May 2020 11:59:16 -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: fix dereference of pointer before it
 has been null checked

On Tue, May 12, 2020 at 06:19:32PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently the assignment of cnt 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 cnt
> is to be used.
> 
> Addresses-Coverity: ("Dereference before null check")
> Fixes: 637ce64e7f57 ("pstore/zone,blk: Add support for pmsg frontend")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  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 c5bf3b9f644f..3cf7d6762c76 100644
> --- a/fs/pstore/zone.c
> +++ b/fs/pstore/zone.c
> @@ -825,7 +825,7 @@ static int notrace psz_record_write(struct pstore_zone *zone,
>  		struct pstore_record *record)
>  {
>  	size_t start, rem;
> -	int cnt = record->size;
> +	int cnt;
>  	bool is_full_data = false;
>  	char *buf = record->buf;

Also here. I'll fix both. Thanks!

-Kees

>  
> @@ -835,6 +835,7 @@ static int notrace psz_record_write(struct pstore_zone *zone,
>  	if (atomic_read(&zone->buffer->datalen) >= zone->buffer_size)
>  		is_full_data = true;
>  
> +	cnt = record->size;
>  	if (unlikely(cnt > zone->buffer_size)) {
>  		buf += cnt - zone->buffer_size;
>  		cnt = zone->buffer_size;
> -- 
> 2.25.1
> 

-- 
Kees Cook