another patch in #for-linus (was Re: [RFC] a corner case of open(2))

[Al Viro]

On Wed, Apr 27, 2016 at 06:34:58AM +0100, Al Viro wrote:
> Fun bugs caught while trying to massage atomic_open()...  Patch below is
> in vfs.git#for-linus (along with two more fixes); I would like to get
> an ACK from Miklos on that one [snip]

Now that Miklos has ACKed that one...  The other fix in there is for alignment
checks in blk_rq_map_user_iov() - also -stable fodder, even though this one
will be a bit more work to backport.  Jens, could you ACK that one?  This is
the patch I'd sent your way several weeks ago (and the one we'd been talking
about at LSFMM):

commit 357f435d8a0d32068c75f3c7176434d992b3adb7
Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date:   Fri Apr 8 19:05:19 2016 -0400

    fix the copy vs. map logics in blk_rq_map_user_iov()
    
    Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

diff --git a/block/blk-map.c b/block/blk-map.c
index a54f054..b9f88b77 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -9,24 +9,6 @@
 
 #include "blk.h"
 
-static bool iovec_gap_to_prv(struct request_queue *q,
-			     struct iovec *prv, struct iovec *cur)
-{
-	unsigned long prev_end;
-
-	if (!queue_virt_boundary(q))
-		return false;
-
-	if (prv->iov_base == NULL && prv->iov_len == 0)
-		/* prv is not set - don't check */
-		return false;
-
-	prev_end = (unsigned long)(prv->iov_base + prv->iov_len);
-
-	return (((unsigned long)cur->iov_base & queue_virt_boundary(q)) ||
-		prev_end & queue_virt_boundary(q));
-}
-
 int blk_rq_append_bio(struct request_queue *q, struct request *rq,
 		      struct bio *bio)
 {
@@ -125,31 +107,18 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
 			struct rq_map_data *map_data,
 			const struct iov_iter *iter, gfp_t gfp_mask)
 {
-	struct iovec iov, prv = {.iov_base = NULL, .iov_len = 0};
-	bool copy = (q->dma_pad_mask & iter->count) || map_data;
+	bool copy = false;
+	unsigned long align = q->dma_pad_mask | queue_dma_alignment(q);
 	struct bio *bio = NULL;
 	struct iov_iter i;
 	int ret;
 
-	if (!iter || !iter->count)
-		return -EINVAL;
-
-	iov_for_each(iov, i, *iter) {
-		unsigned long uaddr = (unsigned long) iov.iov_base;
-
-		if (!iov.iov_len)
-			return -EINVAL;
-
-		/*
-		 * Keep going so we check length of all segments
-		 */
-		if ((uaddr & queue_dma_alignment(q)) ||
-		    iovec_gap_to_prv(q, &prv, &iov))
-			copy = true;
-
-		prv.iov_base = iov.iov_base;
-		prv.iov_len = iov.iov_len;
-	}
+	if (map_data)
+		copy = true;
+	else if (iov_iter_alignment(iter) & align)
+		copy = true;
+	else if (queue_virt_boundary(q))
+		copy = queue_virt_boundary(q) & iov_iter_gap_alignment(iter);
 
 	i = *iter;
 	do {
diff --git a/include/linux/uio.h b/include/linux/uio.h
index fd9bcfe..1b5d1cd 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -87,6 +87,7 @@ size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i);
 size_t copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i);
 size_t iov_iter_zero(size_t bytes, struct iov_iter *);
 unsigned long iov_iter_alignment(const struct iov_iter *i);
+unsigned long iov_iter_gap_alignment(const struct iov_iter *i);
 void iov_iter_init(struct iov_iter *i, int direction, const struct iovec *iov,
 			unsigned long nr_segs, size_t count);
 void iov_iter_kvec(struct iov_iter *i, int direction, const struct kvec *kvec,
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 5fecddc..ca5316e 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -569,6 +569,25 @@ unsigned long iov_iter_alignment(const struct iov_iter *i)
 }
 EXPORT_SYMBOL(iov_iter_alignment);
 
+unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
+{
+        unsigned long res = 0;
+	size_t size = i->count;
+	if (!size)
+		return 0;
+
+	iterate_all_kinds(i, size, v,
+		(res |= (!res ? 0 : (unsigned long)v.iov_base) |
+			(size != v.iov_len ? size : 0), 0),
+		(res |= (!res ? 0 : (unsigned long)v.bv_offset) |
+			(size != v.bv_len ? size : 0)),
+		(res |= (!res ? 0 : (unsigned long)v.iov_base) |
+			(size != v.iov_len ? size : 0))
+		);
+		return res;
+}
+EXPORT_SYMBOL(iov_iter_gap_alignment);
+
 ssize_t iov_iter_get_pages(struct iov_iter *i,
 		   struct page **pages, size_t maxsize, unsigned maxpages,
 		   size_t *start)