diff mbox series

[v2] udmabuf: Fix a potential (and unlikely) access to unallocated memory

Message ID f75d0426a17b57dbddacd7da345c1c62a3dbb7ce.1708278363.git.christophe.jaillet@wanadoo.fr
State New
Headers
Series [v2] udmabuf: Fix a potential (and unlikely) access to unallocated memory |

Commit Message

Christophe JAILLET Feb. 18, 2024, 5:46 p.m. UTC 
  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() would access to memory beyond 'list'.

Use memdup_array_user() which checks for overflow.

While at it, include <linux/string.h>.

Fixes: fbb0de795078 ("Add udmabuf misc device")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
v2: - Use memdup_array_user()   [Kees Cook]
    - Use sizeof(*list)   [Gustavo A. R. Silva]
    - Add include <linux/string.h>

v1: https://lore.kernel.org/all/3e37f05c7593f1016f0a46de188b3357cbbd0c0b.1695060389.git.christophe.jaillet@wanadoo.fr/

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
 drivers/dma-buf/udmabuf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

Dan Carpenter Feb. 19, 2024, 8:37 a.m. UTC | #1 
On Sun, Feb 18, 2024 at 06:46:44PM +0100, Christophe JAILLET wrote:
> If 'list_limit' is set to a very high value, 'lsize' computation could
> overflow if 'head.count' is big enough.
> 

The "list_limit" is set via module parameter so if you set that high
enough to lead to an integer overflow then you kind of deserve what
you get.

This patch is nice for kernel hardening and making the code easier to
read/audit but the real world security impact is negligible.

regards,
dan carpenter
Christophe JAILLET Feb. 19, 2024, 5:59 p.m. UTC | #2 
Le 19/02/2024 à 09:37, Dan Carpenter a écrit :
> On Sun, Feb 18, 2024 at 06:46:44PM +0100, Christophe JAILLET wrote:
>> If 'list_limit' is set to a very high value, 'lsize' computation could
>> overflow if 'head.count' is big enough.
>>
> 
> The "list_limit" is set via module parameter so if you set that high
> enough to lead to an integer overflow then you kind of deserve what
> you get.
> 
> This patch is nice for kernel hardening and making the code easier to
> read/audit but the real world security impact is negligible.

Agreed.

That is what I meant by "and unlikely".
Maybe the commit message could be more explicit if needed.

Let me know if ok as-is or if I should try to re-word the description.

CJ

> 
> regards,
> dan carpenter
> 
> 
>
Gustavo A. R. Silva Feb. 19, 2024, 6:47 p.m. UTC | #3 
On 2/18/24 11:46, 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() would access to memory beyond 'list'.
> 
> Use memdup_array_user() which checks for overflow.
> 
> While at it, include <linux/string.h>.
> 
> Fixes: fbb0de795078 ("Add udmabuf misc device")'

I don't think this tag is needed in this case.

Also, please, CC linux-hardening next time.

> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>

In any case, LGTM:

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks!
--
Gustavo

> ---
> v2: - Use memdup_array_user()   [Kees Cook]
>      - Use sizeof(*list)   [Gustavo A. R. Silva]
>      - Add include <linux/string.h>
> 
> v1: https://lore.kernel.org/all/3e37f05c7593f1016f0a46de188b3357cbbd0c0b.1695060389.git.christophe.jaillet@wanadoo.fr/
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
>   drivers/dma-buf/udmabuf.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index c40645999648..5728948ea6f2 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -11,6 +11,7 @@
>   #include <linux/module.h>
>   #include <linux/shmem_fs.h>
>   #include <linux/slab.h>
> +#include <linux/string.h>
>   #include <linux/udmabuf.h>
>   #include <linux/vmalloc.h>
>   #include <linux/iosys-map.h>
> @@ -314,14 +315,13 @@ 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)),
> +				 sizeof(*list), head.count);
>   	if (IS_ERR(list))
>   		return PTR_ERR(list);
>
Dan Carpenter Feb. 20, 2024, 5:11 a.m. UTC | #4 
On Mon, Feb 19, 2024 at 06:59:02PM +0100, Christophe JAILLET wrote:
> Le 19/02/2024 à 09:37, Dan Carpenter a écrit :
> > On Sun, Feb 18, 2024 at 06:46:44PM +0100, Christophe JAILLET wrote:
> > > If 'list_limit' is set to a very high value, 'lsize' computation could
> > > overflow if 'head.count' is big enough.
> > > 
> > 
> > The "list_limit" is set via module parameter so if you set that high
> > enough to lead to an integer overflow then you kind of deserve what
> > you get.
> > 
> > This patch is nice for kernel hardening and making the code easier to
> > read/audit but the real world security impact is negligible.
> 
> Agreed.
> 
> That is what I meant by "and unlikely".
> Maybe the commit message could be more explicit if needed.
> 
> Let me know if ok as-is or if I should try to re-word the description.

No, it's fine.  But in the future if there is an integer overflow then
lets mention in the commit message who it affects or what the impact is.

regards,
dan carpenter
diff mbox series

Patch

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index c40645999648..5728948ea6f2 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -11,6 +11,7 @@ 
 #include <linux/module.h>
 #include <linux/shmem_fs.h>
 #include <linux/slab.h>
+#include <linux/string.h>
 #include <linux/udmabuf.h>
 #include <linux/vmalloc.h>
 #include <linux/iosys-map.h>
@@ -314,14 +315,13 @@  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)),
+				 sizeof(*list), head.count);
 	if (IS_ERR(list))
 		return PTR_ERR(list);