fix unbalanced page refcounting in bio_map_user_iov

commit 95d78c28b5a85bacbc29b8dba7c04babb9b0d467 upstream.

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.

Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/block/bio.c b/block/bio.c
index 14263fab94d3..68bbc835bacc 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1320,6 +1320,7 @@ 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;
@@ -1334,6 +1335,13 @@ 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;
                 }