[PATCH v2 1/2] zram: fix use-after-free in zram_bvec_write_partial()

[Cunlong Li]

zram_read_page() picks the sync or async backing device read path
based on whether the parent bio is NULL.  zram_bvec_write_partial()
passes its parent bio down, so for ZRAM_WB slots the read is
dispatched asynchronously and zram_read_page() returns 0 while the
bio is still in flight.  The caller then runs memcpy_from_bvec(),
zram_write_page() and __free_page() on the buffer, leaving the
async read to write into a freed page.

zram_bvec_read_partial() was switched to NULL in commit 4e3c87b9421d
("zram: fix synchronous reads") for the same reason; the
write_partial counterpart was missed.

Fixes: 4e3c87b9421d ("zram: fix synchronous reads")
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Cunlong Li <shenxiaogll@xxxxxxxxx>
---
 drivers/block/zram/zram_drv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index aebc710f0d6a..b23a8bbb687c 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -2333,7 +2333,7 @@ static int zram_bvec_write_partial(struct zram *zram, struct bio_vec *bvec,
 	if (!page)
 		return -ENOMEM;
 
-	ret = zram_read_page(zram, page, index, bio);
+	ret = zram_read_page(zram, page, index, NULL);
 	if (!ret) {
 		memcpy_from_bvec(page_address(page) + offset, bvec);
 		ret = zram_write_page(zram, page, index);

-- 
2.30.2