zram: fix use-after-free in zram_bvec_write_partial()

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.

Link: https://lore.kernel.org/20260528-zram-v3-1-cab86eef8764@gmail.com
Fixes: 8e654f8fbff5 ("zram: read page from backing device")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Cunlong Li <shenxiaogll@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Yisheng Xie <xieyisheng1@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 07111455eecff7ab66b7e2b9c7da2f831b795fbb..e11ee1ed38320c85af2a64663564d272b72579f4 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -2337,7 +2337,7 @@ 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);