[PATCH v2 1/2] udmabuf: Fix list length overflow check

[Val Packett <val@invisiblethingslab.com>]

The udmabuf list length limit was made configurable, creating the
possibility for integer overflow that was not properly detected.
If the system administrator set the udmabuf.list_limit tunable to
a large value like INT_MAX, that would allow udmabuf users to submit
a list whose length would overflow the u32 length variable.

Use memdup_array_user() instead of raw memdup_user() to make the length
calculation an overflow-checked multiplication.

Cc: stable@vger.kernel.org
Fixes: 2e717a55982a ("udmabuf: configurable list_limit and size_limit_mb")
Suggested-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Val Packett <val@invisiblethingslab.com>
---
 drivers/dma-buf/udmabuf.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index df6dd0046242..654ebe7f6b3f 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -470,14 +470,13 @@ static long udmabuf_ioctl_create_list(struct file *filp, unsigned long arg)
 	struct udmabuf_create_list head;
 	struct udmabuf_create_item *list;
 	int ret = -EINVAL;
-	u32 lsize;
 
 	if (copy_from_user(&head, (void __user *)arg, sizeof(head)))
 		return -EFAULT;
 	if (head.count > list_limit)
 		return -EINVAL;
-	lsize = sizeof(struct udmabuf_create_item) * head.count;
-	list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
+	list = memdup_array_user((void __user *)(arg + sizeof(head)),
+				head.count, sizeof(struct udmabuf_create_item));
 	if (IS_ERR(list))
 		return PTR_ERR(list);
 
-- 
2.55.0