linux-kernel - Re: [PATCH v2] block: fix possible NULL dereference

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Message-ID: <56FE87DF.3000603@kernel.dk>
Date:	Fri, 1 Apr 2016 08:38:23 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
	Johannes Thumshirn <jthumshirn@...e.de>
Subject: Re: [PATCH v2] block: fix possible NULL dereference

On 04/01/2016 08:34 AM, Sudip Mukherjee wrote:
> We were checking for iter to be NULL after dereferencing it. There is
> actually no need to check for iter to be NULL as all the callers of
> blk_rq_map_user_iov() does call it with a valid pointer to
> struct iov_iter.
> But as iter->count can be NULL so the assignment to copy is being done
> after checking for it.
>
> Signed-off-by: Sudip Mukherjee <sudip.mukherjee@...ethink.co.uk>
> ---
>
> v2: removed the check for iter
> v1: moved the assignment to copy after check for iter and iter->count

Your subject is wrong (there's no NULL deref). Ditto for the commit 
message - it can be zero, not NULL. The latter would imply a memory 
address, but it's just an integer.

-- 
Jens Axboe