The patch titled Subject: zram: refuse to use zero sized block device as backing device has been added to the -mm mm-hotfixes-unstable branch. Its filename is zram-refuse-to-use-zero-sized-block-device-as-backing-device.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

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: Kairui Song kasong@tencent.com Subject: zram: refuse to use zero sized block device as backing device Date: Thu, 5 Dec 2024 02:02:23 +0800

Patch series "zram: fix backing device setup issue".

This series fixes two bugs of backing device setting:

- ZRAM should reject using a zero sized (or the uninitialized ZRAM device itself) as the backing device. - Fix backing device leaking when removing a uninitialized ZRAM device.

This patch (of 2):

Setting a zero sized block device as backing device is pointless, and one can easily create a recursive loop by setting the uninitialized ZRAM device itself as its own backing device by (zram0 is uninitialized):

echo /dev/zram0 > /sys/block/zram0/backing_dev

It's definitely a wrong config, and the module will pin itself, kernel should refuse doing so in the first place.

By refusing to use zero sized device we avoided misuse cases including this one above.

Link: https://lkml.kernel.org/r/20241204180224.31069-1-ryncsn@gmail.com Link: https://lkml.kernel.org/r/20241204180224.31069-2-ryncsn@gmail.com Fixes: 013bf95a83ec ("zram: add interface to specif backing device") Signed-off-by: Kairui Song kasong@tencent.com Reported-by: Desheng Wu deshengwu@tencent.com Cc: Minchan Kim minchan@kernel.org Cc: Sergey Senozhatsky senozhatsky@chromium.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

drivers/block/zram/zram_drv.c | 6 ++++++ 1 file changed, 6 insertions(+)

--- a/drivers/block/zram/zram_drv.c~zram-refuse-to-use-zero-sized-block-device-as-backing-device +++ a/drivers/block/zram/zram_drv.c @@ -614,6 +614,12 @@ static ssize_t backing_dev_store(struct }

nr_pages = i_size_read(inode) >> PAGE_SHIFT; + /* Refuse to use zero sized device (also prevents self reference) */ + if (!nr_pages) { + err = -EINVAL; + goto out; + } + bitmap_sz = BITS_TO_LONGS(nr_pages) * sizeof(long); bitmap = kvzalloc(bitmap_sz, GFP_KERNEL); if (!bitmap) { _

Patches currently in -mm which might be from kasong@tencent.com are

zram-refuse-to-use-zero-sized-block-device-as-backing-device.patch zram-fix-uninitialized-zram-not-releasing-backing-device.patch