linux-kernel - Re: [4.10, panic, regression] iscsi: null pointer deref at iscsi_tcp_segment

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Date:   Thu, 22 Dec 2016 07:18:27 +0100
From:   Christoph Hellwig <hch@....de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Dave Chinner <david@...morbit.com>,
        Chris Leech <cleech@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lee Duncan <lduncan@...e.com>, open-iscsi@...glegroups.com,
        Linux SCSI List <linux-scsi@...r.kernel.org>,
        linux-block@...r.kernel.org, Christoph Hellwig <hch@....de>
Subject: Re: [4.10, panic, regression] iscsi: null pointer deref at
        iscsi_tcp_segment_done+0x20d/0x2e0

On Wed, Dec 21, 2016 at 03:19:15PM -0800, Linus Torvalds wrote:
> Looking around a bit, the only even halfway suspicious scatterlist
> initialization thing I see is commit f9d03f96b988 ("block: improve
> handling of the magic discard payload") which used to have a magic
> hack wrt !bio->bi_vcnt, and that got removed. See __blk_bios_map_sg(),
> now it does __blk_bvec_map_sg() instead.

But that check was only for discard (and discard-like) bios which
had the maic single page that sometimes was unused attached.

For "normal" bios the for_each_segment loop iterates over bi_vcnt,
so it will be ignored anyway.  That being said both I and the lists
got CCed halfway through the thread and I haven't seen the original
report, so I'm not really sure what's going on here anyway.