Different iovec may use one same page, then 'pages' array filled
by iov_iter_get_pages() may get reference of the same page several
times. If some elements in 'pages' can be merged to same page in
one bvec by bio_add_page(), bio_release_pages() only drops the
page's reference once.
This way causes page leak reported by David Gibson.
This issue can be triggered since 576ed913 ("block: use bio_add_page in
bio_iov_iter_get_pages").
Fixes the issue by putting the page's ref if it is merged to same page.
Cc: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
Cc: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
Cc: linux-xfs@xxxxxxxxxxxxxxx
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Link: https://lkml.org/lkml/2019/4/23/64
Fixes: 576ed913 ("block: use bio_add_page in bio_iov_iter_get_pages")
Reported-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
block/bio.c | 12 ++++++++++--
include/linux/bio.h | 8 ++++++++
2 files changed, 18 insertions(+), 2 deletions(-)
diff --git a/block/bio.c b/block/bio.c
index 39e3b931dc3b..358ccb5086e6 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -652,6 +652,9 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
return false;
if (pfn_to_page(PFN_DOWN(vec_end_addr)) + 1 != page)
return false;
+ /* drop page ref if the page has been added and user asks to do that */
+ } else if (flags & BVEC_MERGE_PUT_SAME_PAGE) {
+ put_page(page);
}
WARN_ON_ONCE((flags & BVEC_MERGE_TO_SAME_PAGE) &&
@@ -924,8 +927,13 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
struct page *page = pages[i];
len = min_t(size_t, PAGE_SIZE - offset, left);
- if (WARN_ON_ONCE(bio_add_page(bio, page, len, offset) != len))
- return -EINVAL;
+
+ if (!__bio_try_merge_page(bio, page, len, offset,
+ BVEC_MERGE_PUT_SAME_PAGE)) {
+ if (WARN_ON_ONCE(bio_full(bio)))
+ return -EINVAL;
+ __bio_add_page(bio, page, len, offset);
+ }
offset = 0;
}
diff --git a/include/linux/bio.h b/include/linux/bio.h
index ee18895431ba..0168bc5df8e4 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -428,6 +428,14 @@ enum bvec_merge_flags {
* bvec
*/
BVEC_MERGE_TO_SAME_PAGE = BIT(0),
+
+ /*
+ * put refcount of bio's last page if the start page to add is
+ * same with bio's last page. If user gets refcount of every
+ * page added to bio before calling bio_add_page, please consider
+ * to use this flag for avoiding page leak
+ */
+ BVEC_MERGE_PUT_SAME_PAGE = BIT(1),
};
extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
--
2.20.1
