Re: [PATCH] udmabuf: Fix a potential (and unlikely) access to unallocated memory

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On 9/18/23 12:46, Christophe JAILLET wrote:
If 'list_limit' is set to a very high value, 'lsize' computation could
overflow if 'head.count' is big enough.

In such a case, udmabuf_create() will access to memory beyond 'list'.

Use size_mul() to saturate the value, and have memdup_user() fail.

Fixes: fbb0de795078 ("Add udmabuf misc device")
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
---
  drivers/dma-buf/udmabuf.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index c40645999648..fb4c4b5b3332 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -314,13 +314,13 @@ 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;
+	size_t 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;
+	lsize = size_mul(sizeof(struct udmabuf_create_item), head.count);
  	list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
  	if (IS_ERR(list))
  		return PTR_ERR(list);

How about this, and we get rid of `lsize`:

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index c40645999648..5cf9d849aaa8 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -314,14 +314,13 @@ 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_user((void __user *)(arg + sizeof(head)),
+                          size_mul(sizeof(*list), head.count));
        if (IS_ERR(list))
                return PTR_ERR(list);


--
Gustavo



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