zram: refuse to use zero sized block device as backing device

commit be48c412f6ebf38849213c19547bc6d5b692b5e5 upstream.

Patch series "zram: fix backing device setup issue", v2.

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/20241209165717.94215-1-ryncsn@gmail.com
Link: https://lkml.kernel.org/r/20241209165717.94215-2-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>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 966aab902d19a6c1a4720fc78138761e267b23af..102c78cfc0dbd2267ec39d2e0897fd9f38871665 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -530,6 +530,12 @@ static ssize_t backing_dev_store(struct device *dev,
        }
 
        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) {