[PATCH] block: fix "check bi_size overflow before merge"

From: Andreas Gruenbacher <agruenba@redhat.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Junichi Nomura <j-nomura@ce.jp.nec.com>,
	Christoph Hellwig <hch@lst.de>, Ming Lei <ming.lei@redhat.com>,
	Hannes Reinecke <hare@suse.de>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	Andreas Gruenbacher <agruenba@redhat.com>,
	stable@vger.kernel.org
Subject: [PATCH] block: fix "check bi_size overflow before merge"
Date: Mon,  9 Dec 2019 20:11:14 +0100	[thread overview]
Message-ID: <20191209191114.17266-1-agruenba@redhat.com> (raw)

This partially reverts commit e3a5d8e386c3fb973fa75f2403622a8f3640ec06.

Commit e3a5d8e386c3 ("check bi_size overflow before merge") adds a bio_full
check to __bio_try_merge_page.  This will cause __bio_try_merge_page to fail
when the last bi_io_vec has been reached.  Instead, what we want here is only
the bi_size overflow check.

Fixes: e3a5d8e386c3 ("block: check bi_size overflow before merge")
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 block/bio.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index 9d54aa37ce6c..a5d75f6bf4c7 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -754,10 +754,12 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
 	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
 		return false;
 
-	if (bio->bi_vcnt > 0 && !bio_full(bio, len)) {
+	if (bio->bi_vcnt > 0) {
 		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
 
 		if (page_is_mergeable(bv, page, len, off, same_page)) {
+			if (bio->bi_iter.bi_size > UINT_MAX - len)
+				return false;
 			bv->bv_len += len;
 			bio->bi_iter.bi_size += len;
 			return true;
-- 
2.20.1

