linux-kernel - Re: [PATCH 2/2] dax: fix bdev NULL pointer dereferences

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Message-ID: <CAPcyv4jMMYEoq6gHbcy_HGzVua4PonzQ+X+X4EHRE1X=qeAM0Q@mail.gmail.com>
Date:	Thu, 28 Jan 2016 12:21:39 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH 2/2] dax: fix bdev NULL pointer dereferences

On Thu, Jan 28, 2016 at 11:35 AM, Ross Zwisler
<ross.zwisler@...ux.intel.com> wrote:
> There are a number of places in dax.c that look up the struct block_device
> associated with an inode.  Previously this was done by just using
> inode->i_sb->s_bdev.  This is correct for inodes that exist within the
> filesystems supported by DAX (ext2, ext4 & XFS), but when running DAX
> against raw block devices this value is NULL.  This causes NULL pointer
> dereferences when these block_device pointers are used.
>
> Instead, for raw block devices we need to look up the struct block_device
> using I_BDEV().  This patch fixes all the block_device lookups in dax.c so
> that they work properly for both filesystems and raw block devices.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>

It's a bit odd to check if it is a raw device inode in
dax_clear_blocks() since there's no use case to clear blocks in that
case, but I can't think of a better alternative.

Acked-by: Dan Williams <dan.j.williams@...el.com>