fix unbalanced page refcounting in bio_map_user_iov

bio_map_user_iov and bio_unmap_user do unbalanced pages refcounting if
IO vector has small consecutive buffers belonging to the same page.
bio_add_pc_page merges them into one, but the page reference is never
dropped.

Cc: stable@vger.kernel.org
Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
(cherry picked from commit 95d78c28b5a85bacbc29b8dba7c04babb9b0d467)

Orabug: 27062562
CVE: CVE-2017-12190

Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>
Reviewed-by: Ethan Zhao <ethan.zhao@oracle.com>

diff --git a/block/bio.c b/block/bio.c
index 6e31ceacd4a906000cdfc5efcc20549da47e7952..f4cbd84b0abfe3f9be61dcb1ec77e5750b79ad5e 100644 (file)
--- a/block/bio.c
+++ b/block/bio.c
@@ -1367,6 +1367,7 @@ struct bio *bio_map_user_iov(struct request_queue *q,
                offset = uaddr & ~PAGE_MASK;
                for (j = cur_page; j < page_limit; j++) {
                        unsigned int bytes = PAGE_SIZE - offset;
+                       unsigned short prev_bi_vcnt = bio->bi_vcnt;
 
                        if (len <= 0)
                                break;
@@ -1381,6 +1382,13 @@ struct bio *bio_map_user_iov(struct request_queue *q,
                                            bytes)
                                break;
 
+                       /*
+                        * check if vector was merged with previous
+                        * drop page reference if needed
+                        */
+                       if (bio->bi_vcnt == prev_bi_vcnt)
+                               put_page(pages[j]);
+
                        len -= bytes;
                        offset = 0;
                }