From: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Date: Fri, 22 Sep 2017 01:18:39 -0400
Subject: fix unbalanced page refcounting in bio_map_user_iov
References: bsc#1062568 CVE-2017-12190
Git-commit: 95d78c28b5a85bacbc29b8dba7c04babb9b0d467
Patch-mainline: v4.14-rc5
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>
Acked-by: Johannes Thumshirn <jthumshirn@suse.de>
---
block/bio.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/block/bio.c b/block/bio.c
index b38e962fa83e..0d6439e89acb 100644
--- a/block/bio.c
+++ b/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;
}
--
2.12.3