[PATCH 1/1] null_blk: Use u64 to avoid overflow in null_alloc_dev()

[Zhu Yanjun <yanjun.zhu@linux.dev>]

The member variable size in struct nullb_device is the type
unsigned long, and the module parameter g_gb is the type int.
In 32 bit architecture, unsigned long has 32 bit. This
introduces overflow risks.

Use the type u64 in struct nullb_device and configfs. This
can avoid overflow risks.

Fixes: 2984c8684f96 ("nullb: factor disk parameters")
Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
---
 drivers/block/null_blk/main.c     | 23 +++++++++++++++++++++--
 drivers/block/null_blk/null_blk.h |  2 +-
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 2f0431e42c49..88c6d6277d09 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -289,6 +289,11 @@ static inline ssize_t nullb_device_ulong_attr_show(unsigned long val,
 	return snprintf(page, PAGE_SIZE, "%lu\n", val);
 }
 
+static inline ssize_t nullb_device_u64_attr_show(u64 val, char *page)
+{
+	return snprintf(page, PAGE_SIZE, "%llu\n", val);
+}
+
 static inline ssize_t nullb_device_bool_attr_show(bool val, char *page)
 {
 	return snprintf(page, PAGE_SIZE, "%u\n", val);
@@ -322,6 +327,20 @@ static ssize_t nullb_device_ulong_attr_store(unsigned long *val,
 	return count;
 }
 
+static ssize_t nullb_device_u64_attr_store(u64 *val, const char *page,
+	size_t count)
+{
+	int result;
+	u64 tmp;
+
+	result = kstrtou64(page, 0, &tmp);
+	if (result < 0)
+		return result;
+
+	*val = tmp;
+	return count;
+}
+
 static ssize_t nullb_device_bool_attr_store(bool *val, const char *page,
 	size_t count)
 {
@@ -438,7 +457,7 @@ static int nullb_apply_poll_queues(struct nullb_device *dev,
 	return ret;
 }
 
-NULLB_DEVICE_ATTR(size, ulong, NULL);
+NULLB_DEVICE_ATTR(size, u64, NULL);
 NULLB_DEVICE_ATTR(completion_nsec, ulong, NULL);
 NULLB_DEVICE_ATTR(submit_queues, uint, nullb_apply_submit_queues);
 NULLB_DEVICE_ATTR(poll_queues, uint, nullb_apply_poll_queues);
@@ -762,7 +781,7 @@ static struct nullb_device *null_alloc_dev(void)
 		return NULL;
 	}
 
-	dev->size = g_gb * 1024;
+	dev->size = (u64)g_gb * 1024;
 	dev->completion_nsec = g_completion_nsec;
 	dev->submit_queues = g_submit_queues;
 	dev->prev_submit_queues = g_submit_queues;
diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
index a7bb32f73ec3..e30c011909ad 100644
--- a/drivers/block/null_blk/null_blk.h
+++ b/drivers/block/null_blk/null_blk.h
@@ -74,7 +74,7 @@ struct nullb_device {
 	bool need_zone_res_mgmt;
 	spinlock_t zone_res_lock;
 
-	unsigned long size; /* device size in MB */
+	u64 size; /* device size in MB */
 	unsigned long completion_nsec; /* time in ns to complete a request */
 	unsigned long cache_size; /* disk cache size in MB */
 	unsigned long zone_size; /* zone size in MB if device is zoned */
-- 
2.39.2