[PATCH] bpf: fix: address of local auto-variable assigned to a function parameter.

[PATCH] bpf: fix: address of local auto-variable assigned to a function parameter.

[YANG LI]

Assigning local variable txq to the outputting parameter xdp->txq is not
safe, txq will be released after the end of the function call. 
Then the result of using xdp is unpredictable.

Fix this error by defining the struct xdp_txq_info in function
dev_map_run_prog() as a static type.

Signed-off-by: YANG LI <abaci-bugfix@linux.alibaba.com>
Reported-by: Abaci <abaci@linux.alibaba.com>
---
 kernel/bpf/devmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index f6e9c68..af6f004 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -454,7 +454,7 @@ static struct xdp_buff *dev_map_run_prog(struct net_device *dev,
 					 struct xdp_buff *xdp,
 					 struct bpf_prog *xdp_prog)
 {
-	struct xdp_txq_info txq = { .dev = dev };
+	static struct xdp_txq_info txq = { .dev = dev };
 	u32 act;
 
 	xdp_set_data_meta_invalid(xdp);
-- 
1.8.3.1

Re: [PATCH] bpf: fix: address of local auto-variable assigned to a function parameter.

[Yonghong Song]

On 12/23/20 11:01 PM, YANG LI wrote:
> Assigning local variable txq to the outputting parameter xdp->txq is not
> safe, txq will be released after the end of the function call.
> Then the result of using xdp is unpredictable.
> 
> Fix this error by defining the struct xdp_txq_info in function
> dev_map_run_prog() as a static type.
> 
> Signed-off-by: YANG LI <abaci-bugfix@linux.alibaba.com>
> Reported-by: Abaci <abaci@linux.alibaba.com>
> ---
>   kernel/bpf/devmap.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index f6e9c68..af6f004 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -454,7 +454,7 @@ static struct xdp_buff *dev_map_run_prog(struct net_device *dev,
>   					 struct xdp_buff *xdp,
>   					 struct bpf_prog *xdp_prog)
>   {
> -	struct xdp_txq_info txq = { .dev = dev };
> +	static struct xdp_txq_info txq = { .dev = dev };
>   	u32 act;
>   
>   	xdp_set_data_meta_invalid(xdp);

exposing txq outside the routine with 'static' definition is not
a good practice. maybe just reset xdp->txq = NULl right before
function return?

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index f6e9c68afdd4..50f5c20a33a3 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -475,6 +475,7 @@ static struct xdp_buff *dev_map_run_prog(struct 
net_device *dev,
         }

         xdp_return_buff(xdp);
+       xdp->txq = NULL;
         return NULL;
  }

-bash-4.4$

Re: [PATCH] bpf: fix: address of local auto-variable assigned to a function parameter.

[David Ahern]

On 12/24/20 12:01 AM, YANG LI wrote:
> Assigning local variable txq to the outputting parameter xdp->txq is not
> safe, txq will be released after the end of the function call. 
> Then the result of using xdp is unpredictable.

txq can only be accessed in this devmap context. Was it actually hit
during runtime or is this report based on code analysis?


> 
> Fix this error by defining the struct xdp_txq_info in function
> dev_map_run_prog() as a static type.
> 
> Signed-off-by: YANG LI <abaci-bugfix@linux.alibaba.com>
> Reported-by: Abaci <abaci@linux.alibaba.com>
> ---
>  kernel/bpf/devmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index f6e9c68..af6f004 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -454,7 +454,7 @@ static struct xdp_buff *dev_map_run_prog(struct net_device *dev,
>  					 struct xdp_buff *xdp,
>  					 struct bpf_prog *xdp_prog)
>  {
> -	struct xdp_txq_info txq = { .dev = dev };
> +	static struct xdp_txq_info txq = { .dev = dev };
>  	u32 act;
>  
>  	xdp_set_data_meta_invalid(xdp);
>