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

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Message-ID: <20160401151828.GA20149@sudip-tp>
Date:	Fri, 1 Apr 2016 16:18:28 +0100
From:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:	Jens Axboe <axboe@...nel.dk>
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 Fri, Apr 01, 2016 at 08:38:23AM -0600, Jens Axboe wrote:
> 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.

oops. I should have checked. I wanted to keep the commit message similar to
v1. I will send a v3 for this.

regards
sudip