Patch "fix unbalanced page refcounting in bio_map_user_iov" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

fix unbalanced page refcounting in bio_map_user_iov

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fix-unbalanced-page-refcounting-in-bio_map_user_iov.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Vitaly Mayatskikh <[email protected]>
Date: Fri, 22 Sep 2017 01:18:39 -0400
Subject: fix unbalanced page refcounting in bio_map_user_iov

From: Vitaly Mayatskikh <[email protected]>

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.

---
 block/bio.c |    8 ++++++++
 1 file changed, 8 insertions(+)

@@ -1320,6 +1320,7 @@ struct bio *bio_map_user_iov(struct requ
 		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 requ
 					    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;
 		}

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/fix-unbalanced-page-refcounting-in-bio_map_user_iov.patch