+ zram-fix-use-after-free-in-zram_bvec_write_partial.patch added to mm-hotfixes-unstable branch

+ zram-fix-use-after-free-in-zram_bvec_write_partial.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: zram: fix use-after-free in zram_bvec_write_partial()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     zram-fix-use-after-free-in-zram_bvec_write_partial.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-fix-use-after-free-in-zram_bvec_write_partial.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Cunlong Li <shenxiaogll@gmail.com>
Subject: zram: fix use-after-free in zram_bvec_write_partial()
Date: Thu, 28 May 2026 10:48:44 +0800

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>
---

 drivers/block/zram/zram_drv.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/block/zram/zram_drv.c~zram-fix-use-after-free-in-zram_bvec_write_partial
+++ a/drivers/block/zram/zram_drv.c
@@ -2337,7 +2337,7 @@ static int zram_bvec_write_partial(struc
 	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);
_

Patches currently in -mm which might be from shenxiaogll@gmail.com are

zram-fix-use-after-free-in-zram_bvec_write_partial.patch
zram-drop-unused-bio-parameter-from-write-helpers.patch