diff mbox series

[v2,1/2] zram: refuse to use zero sized block device as backing device

Message ID 20241209165717.94215-2-ryncsn@gmail.com (mailing list archive)
State New, archived
Headers show
Series zram: fix backing device setup issue | expand

Commit Message

Kairui Song Dec. 9, 2024, 4:57 p.m. UTC 
From: Kairui Song <kasong@tencent.com>

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.

Fixes: 013bf95a83ec ("zram: add interface to specif backing device")
Reported-by: Desheng Wu <deshengwu@tencent.com>
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: stable@vger.kernel.org
---
 drivers/block/zram/zram_drv.c | 6 ++++++
 1 file changed, 6 insertions(+)
diff mbox series

Patch

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 3dee026988dc..e86cc3d2f4d2 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -614,6 +614,12 @@  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) {