[PATCH] block: Fix potential page reference leak in __bio_iov_iter_get_pages()

[PATCH] block: Fix potential page reference leak in __bio_iov_iter_get_pages()

[Miaohe Lin]

When bio is full, __bio_iov_iter_get_pages() would return error directly
while left page reference still held in pages. Release these references.
Also advance the iov_iter according to what we have done successfully.

Fixes: 576ed9135489 ("block: use bio_add_page in bio_iov_iter_get_pages")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 block/bio.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index a9931f23d933..e113073958cb 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1023,7 +1023,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 				put_page(page);
 		} else {
 			if (WARN_ON_ONCE(bio_full(bio, len)))
-                                return -EINVAL;
+				goto put_pages;
 			__bio_add_page(bio, page, len, offset);
 		}
 		offset = 0;
@@ -1031,6 +1031,19 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 
 	iov_iter_advance(iter, size);
 	return 0;
+
+put_pages:
+	/* Advance iov_iter to what we have done yet. */
+	iov_iter_advance(iter, size - left);
+	/* Put the page references still held by pages. */
+	for (; left > 0; left -= len, i++) {
+		struct page *page = pages[i];
+
+		len = min_t(size_t, PAGE_SIZE - offset, left);
+		put_page(page);
+		offset = 0;
+	}
+	return -EINVAL;
 }
 
 static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter)
-- 
2.19.1

Re: [PATCH] block: Fix potential page reference leak in __bio_iov_iter_get_pages()

[Christoph Hellwig]

On Tue, Sep 01, 2020 at 08:00:06AM -0400, Miaohe Lin wrote:
> When bio is full, __bio_iov_iter_get_pages() would return error directly
> while left page reference still held in pages. Release these references.
> Also advance the iov_iter according to what we have done successfully.
> 
> Fixes: 576ed9135489 ("block: use bio_add_page in bio_iov_iter_get_pages")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

The WARN_ON means something is fundamentally wrong here.  I think a few
leaked pages are the least of our problems in this case.

Re: [PATCH] block: Fix potential page reference leak in __bio_iov_iter_get_pages()

[linmiaohe]

Christoph Hellwig <hch@infradead.org> wrote:
>On Tue, Sep 01, 2020 at 08:00:06AM -0400, Miaohe Lin wrote:
>> When bio is full, __bio_iov_iter_get_pages() would return error 
>> directly while left page reference still held in pages. Release these references.
>> Also advance the iov_iter according to what we have done successfully.
>> 
>> Fixes: 576ed9135489 ("block: use bio_add_page in 
>> bio_iov_iter_get_pages")
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>
>The WARN_ON means something is fundamentally wrong here.  I think a few leaked pages are the least of our problems in this case.

Yes, WARN_ON means something is fundamentally wrong here. But IMO it's not really a big problem when bio is full.
We should not simply rely on this WARN_ON and we can handle this gracefully.
Thanks.