Re: [PATCH] net/mpls: fix missing NULL check in mpls_valid_fib_dump_req

[Paolo Abeni <pabeni@redhat.com>]

On 3/23/26 8:15 AM, sunichi wrote:
> The attribute tb[RTA_OIF] is dereferenced without verifying if it is NULL.
> If this attribute is missing in the user netlink message, it will cause a
> NULL pointer dereference and kernel panic.
> 
> Add the necessary check before using the pointer to prevent the crash.
> 
> Signed-off-by: sunichi <sunyiqixm@gmail.com>
> ---
>  net/mpls/af_mpls.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
> index d5417688f69e..28bbea30aae3 100644
> --- a/net/mpls/af_mpls.c
> +++ b/net/mpls/af_mpls.c
> @@ -2174,6 +2174,8 @@ static int mpls_valid_fib_dump_req(struct net *net, const struct nlmsghdr *nlh,
>  		int ifindex;
>  
>  		if (i == RTA_OIF) {
> +			if (!tb[i])
> +				return -EINVAL;
>  			ifindex = nla_get_u32(tb[i]);
>  			filter->dev = dev_get_by_index_rcu(net, ifindex);
>  			if (!filter->dev)

If you reorder the check I think it will lead to better code:

---
diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
index b32311f5cbf7..41510dce5329 100644
--- a/net/mpls/af_mpls.c
+++ b/net/mpls/af_mpls.c
@@ -2170,13 +2170,16 @@ static int mpls_valid_fib_dump_req(struct net
*net, const struct nlmsghdr *nlh,
        for (i = 0; i <= RTA_MAX; ++i) {
                int ifindex;

+               if (!tb[i])
+                       continue;
+
                if (i == RTA_OIF) {
                        ifindex = nla_get_u32(tb[i]);
                        filter->dev = dev_get_by_index_rcu(net, ifindex);
                        if (!filter->dev)
                                return -ENODEV;
                        filter->filter_set = 1;
-               } else if (tb[i]) {
+               } else {
                        NL_SET_ERR_MSG_MOD(extack, "Unsupported
attribute in dump request");
                        return -EINVAL;
                }