Harden a few virtio bits

[PATCH v1 3/6] virtio 9p: Fix an overflow

Posted by Alexander Shishkin 2 years, 7 months ago

From: Andi Kleen <ak@linux.intel.com>

tag_len is read as a u16 from the untrusted host. It could overflow
in the memory allocation, which would lead to a too small buffer.

Some later loops use it when extended to 32bit, so they could overflow
the too small buffer.

Make sure to do the arithmetic for the buffer size in 32bit to avoid
wrapping.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: Dominique Martinet <asmadeus@codewreck.org>
Cc: v9fs-developer@lists.sourceforge.net
---
 net/9p/trans_virtio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 3c27ffb781e3..a78e4d80e5ba 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -629,7 +629,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
 		err = -EINVAL;
 		goto out_free_vq;
 	}
-	tag = kzalloc(tag_len + 1, GFP_KERNEL);
+	tag = kzalloc((u32)tag_len + 1, GFP_KERNEL);
 	if (!tag) {
 		err = -ENOMEM;
 		goto out_free_vq;
-- 
2.39.0

Re: [PATCH v1 3/6] virtio 9p: Fix an overflow

Posted by Michael S. Tsirkin 2 years, 7 months ago

On Thu, Jan 19, 2023 at 03:57:18PM +0200, Alexander Shishkin wrote:
> From: Andi Kleen <ak@linux.intel.com>
> 
> tag_len is read as a u16 from the untrusted host. It could overflow
> in the memory allocation, which would lead to a too small buffer.
> 
> Some later loops use it when extended to 32bit, so they could overflow
> the too small buffer.
> 
> Make sure to do the arithmetic for the buffer size in 32bit to avoid
> wrapping.
> 
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
> Cc: Eric Van Hensbergen <ericvh@gmail.com>
> Cc: Latchesar Ionkov <lucho@ionkov.net>
> Cc: Dominique Martinet <asmadeus@codewreck.org>
> Cc: v9fs-developer@lists.sourceforge.net
> ---
>  net/9p/trans_virtio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index 3c27ffb781e3..a78e4d80e5ba 100644
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -629,7 +629,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
>  		err = -EINVAL;
>  		goto out_free_vq;
>  	}
> -	tag = kzalloc(tag_len + 1, GFP_KERNEL);
> +	tag = kzalloc((u32)tag_len + 1, GFP_KERNEL);
>  	if (!tag) {
>  		err = -ENOMEM;
>  		goto out_free_vq;

Hmm are you sure there's a difference in behaviour? I thought C will just
extend the integer to int.

> -- 
> 2.39.0

Re: [PATCH v1 3/6] virtio 9p: Fix an overflow

Posted by Alexander Shishkin 2 years, 7 months ago

"Michael S. Tsirkin" <mst@redhat.com> writes:

> On Thu, Jan 19, 2023 at 03:57:18PM +0200, Alexander Shishkin wrote:
>> From: Andi Kleen <ak@linux.intel.com>
>> 
>> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
>> index 3c27ffb781e3..a78e4d80e5ba 100644
>> --- a/net/9p/trans_virtio.c
>> +++ b/net/9p/trans_virtio.c
>> @@ -629,7 +629,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
>>  		err = -EINVAL;
>>  		goto out_free_vq;
>>  	}
>> -	tag = kzalloc(tag_len + 1, GFP_KERNEL);
>> +	tag = kzalloc((u32)tag_len + 1, GFP_KERNEL);
>>  	if (!tag) {
>>  		err = -ENOMEM;
>>  		goto out_free_vq;
>
> Hmm are you sure there's a difference in behaviour? I thought C will just
> extend the integer to int.

Actually, you're right, integer promotion would extend the original
expression to int. I'll drop this patch also.

Thanks,
--
Alex