On Wed, Jan 11, 2017 at 07:20:13AM -0500, Jeff Layton wrote:
> On Wed, 2017-01-11 at 10:51 +0100, Johannes Thumshirn wrote:
> > Introduce FMODE_SPLICE_READ and FMODE_SPLICE_WRITE. These modes check
> > whether it is legal to read or write a file using splice. Both get
> > automatically set on regular files and are not checked when a 'struct
> > fileoperations' includes the splice_{read,write} methods.
> >
>
> Could you add a description of the problem that this solves? I assume
> you hit a problem trying to splice to/from a non-regular file, but it'd
> be good to know what that problem was.
The problem is that a driver's ->write() is called under KERNEL_DS this way.
This happened for sg and bsg and caused 128394eff 'sg_write()/bsg_write() is
not fit to be called under KERNEL_DS' as well as a0ac402cf 'Don't feed
anything but regular iovec's to blk_rq_map_user_iov'.
There have also been patches for InfiniBand AFAIR doing similar things.
So this is to solve it for future abuses.
HTH,
Johannes
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