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

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Le 18/09/2023 à 05:10, Gustavo A. R. Silva a écrit :


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`:

Keeping or removing lsize is mostly a matter of taste, I think.

Using sizeof(*list) is better.

Let see if there are some other comments, and I'll send a v2.

Thanks for the feed-back.

CJ


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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