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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>
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vtl authored and Al Viro committed Sep 22, 2017
1 parent 899f042 commit 95d78c28b5a85bacbc29b8dba7c04babb9b0d467
Showing with 8 additions and 0 deletions.
  1. +8 −0 block/bio.c
@@ -1383,6 +1383,7 @@ struct bio *bio_map_user_iov(struct request_queue *q,
offset = offset_in_page(uaddr);
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;
@@ -1397,6 +1398,13 @@ 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;
}

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