linux-kernel - Re: scsi: BUG in scsi_init

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Message-ID: <20170219172541.GA29867@infradead.org>
Date:   Sun, 19 Feb 2017 09:25:41 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     James Bottomley <jejb@...ux.vnet.ibm.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>,
        Hannes Reinecke <hare@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: scsi: BUG in scsi_init_io

On Sun, Feb 19, 2017 at 07:15:27AM +0000, Al Viro wrote:
> The root cause is unfixable without access to TARDIS and dose of
> antipsychotics sufficient to prevent /dev/sg API creation.
> 
> What happens is that write to /dev/sg is given a request with non-zero
> ->iovec_count combined with zero ->dxfer_len.  Or with ->dxferp pointing
> to an array full of empty iovecs.
> 
> AFAICS, the minimal fix would be something like this:
> 
> YAMissingSanityCheck in /dev/sg
> 
> write permission to /dev/sg shouldn't be equivalent to the ability to trigger
> BUG_ON() while holding spinlocks...

Looks fine to me:

Reviewed-by: Christoph Hellwig <hch@....de>

The other thing we really need to consider is to finally merge the
SG_IO implementations for /dev/sg with the common block layer one.