commit c6ade20f upstream.

The WRITE SAME to TRIM translation rewrites the DATA OUT buffer.  While
the SCSI code accomodates for this by passing a read-writable buffer
userspace applications don't cater for this behavior.  In fact it can
be used to rewrite e.g. a readonly file through mmap and should be
considered as a security fix.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
[bwh: Backported to 3.2:
 - Open-code blk_rq_is_passthrough()
 - We don't distinguish which field is invaid so goto invalid_fld
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>