4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpato...@redhat.com>

commit 4e870e948fbabf62b78e8410f04c67703e7c816b upstream.

When dm-crypt processes writes, it allocates a new bio in
crypt_alloc_buffer().  The bio is allocated from a bio set and it can
have at most BIO_MAX_PAGES vector entries, however the incoming bio can be
larger (e.g. if it was allocated by bcache).  If the incoming bio is
larger, bio_alloc_bioset() fails and an error is returned.

To avoid the error, we test for a too large bio in the function
crypt_map() and use dm_accept_partial_bio() to split the bio.
dm_accept_partial_bio() trims the current bio to the desired size and
asks DM core to send another bio with the rest of the data.

Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
Signed-off-by: Mike Snitzer <snit...@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/md/dm-crypt.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -1923,6 +1923,13 @@ static int crypt_map(struct dm_target *t
                return DM_MAPIO_REMAPPED;
        }
 
+       /*
+        * Check if bio is too large, split as needed.
+        */
+       if (unlikely(bio->bi_iter.bi_size > (BIO_MAX_PAGES << PAGE_SHIFT)) &&
+           bio_data_dir(bio) == WRITE)
+               dm_accept_partial_bio(bio, ((BIO_MAX_PAGES << PAGE_SHIFT) >> 
SECTOR_SHIFT));
+
        io = dm_per_bio_data(bio, cc->per_bio_data_size);
        crypt_io_init(io, cc, bio, dm_target_offset(ti, 
bio->bi_iter.bi_sector));
        io->ctx.req = (struct skcipher_request *)(io + 1);


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