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Date: Sun, 19 Feb 2017 09:25:41 -0800
From: Christoph Hellwig <hch@infradead.org>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: James Bottomley <jejb@linux.vnet.ibm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Johannes Thumshirn <jthumshirn@suse.de>,
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        syzkaller <syzkaller@googlegroups.com>, Hannes Reinecke <hare@suse.de>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: scsi: BUG in scsi_init_io
Message-ID: <20170219172541.GA29867@infradead.org>
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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@lst.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.