[PATCH 2/2] zram: fix out-of-bounds access in read_block_state()

[Longlong Xia]

From: Longlong Xia <xialonglong@xxxxxxxxxx>

read_block_state() calculates nr_pages before taking dev_lock. If the
device is reset and reinitialized with a smaller disksize before lock
acquisition, nr_pages still describes the old table. The subsequent
loop can then call slot_lock() past the end of the newly allocated
table.

Read disksize after acquiring dev_lock and checking that the device is
initialized. The read lock then keeps the table and its bound stable for
the duration of the scan.

Fixes: c0265342bff4 ("zram: introduce zram memory tracking")
Cc: <stable@xxxxxxxxxxxxxxx>
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Longlong Xia <xialonglong@xxxxxxxxxx>
---
 drivers/block/zram/zram_drv.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 02fd64475a9a..e5f42f56220d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1552,7 +1552,7 @@ static ssize_t read_block_state(struct file *file, char __user *buf,
 	char *kbuf;
 	ssize_t index, written = 0;
 	struct zram *zram = file->private_data;
-	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
+	unsigned long nr_pages;
 
 	kbuf = kvmalloc(count, GFP_KERNEL);
 	if (!kbuf)
@@ -1564,6 +1564,8 @@ static ssize_t read_block_state(struct file *file, char __user *buf,
 		return -EINVAL;
 	}
 
+	nr_pages = zram->disksize >> PAGE_SHIFT;
+
 	for (index = *ppos; index < nr_pages; index++) {
 		int copied;
 
-- 
2.43.0