Re: [PATCH] net: ipv4: fix a memleak in ip_setup_cork

[Eric Dumazet]

On Fri, Jan 26, 2024 at 8:51 AM Zhipeng Lu <alexious@xxxxxxxxxx> wrote:
>
> When inetdev_valid_mtu fails, cork->opt should be freed if it is
> allocated in ip_setup_cork. Otherwise there could be a memleak.
>
> Fixes: 501a90c94510 ("inet: protect against too small mtu values.")
> Signed-off-by: Zhipeng Lu <alexious@xxxxxxxxxx>
> ---
>  net/ipv4/ip_output.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index b06f678b03a1..3215ea07d398 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -1282,6 +1282,7 @@ static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
>  {
>         struct ip_options_rcu *opt;
>         struct rtable *rt;
> +       int free_opt = 0;
>
>         rt = *rtp;
>         if (unlikely(!rt))
> @@ -1297,6 +1298,7 @@ static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
>                                             sk->sk_allocation);
>                         if (unlikely(!cork->opt))
>                                 return -ENOBUFS;
> +                       free_opt = 1;
>                 }
>                 memcpy(cork->opt, &opt->opt, sizeof(struct ip_options) + opt->opt.optlen);
>                 cork->flags |= IPCORK_OPT;
> @@ -1306,8 +1308,13 @@ static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
>         cork->fragsize = ip_sk_use_pmtu(sk) ?
>                          dst_mtu(&rt->dst) : READ_ONCE(rt->dst.dev->mtu);
>
> -       if (!inetdev_valid_mtu(cork->fragsize))
> +       if (!inetdev_valid_mtu(cork->fragsize)) {
> +               if (opt && free_opt) {
> +                       kfree(cork->opt);
> +                       cork->opt = NULL;
> +               }
>                 return -ENETUNREACH;
> +       }
>
>         cork->gso_size = ipc->gso_size;
>
> --
> 2.34.1
>

What about something simpler like :

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index b06f678b03a19b806fd14764a4caad60caf02919..41537d18eecfd6e1163aacc35e047c22468e04e6
100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1287,6 +1287,12 @@ static int ip_setup_cork(struct sock *sk,
struct inet_cork *cork,
        if (unlikely(!rt))
                return -EFAULT;

+       cork->fragsize = ip_sk_use_pmtu(sk) ?
+                        dst_mtu(&rt->dst) : READ_ONCE(rt->dst.dev->mtu);
+
+       if (!inetdev_valid_mtu(cork->fragsize))
+               return -ENETUNREACH;
+
        /*
         * setup for corking.
         */
@@ -1303,12 +1309,6 @@ static int ip_setup_cork(struct sock *sk,
struct inet_cork *cork,
                cork->addr = ipc->addr;
        }

-       cork->fragsize = ip_sk_use_pmtu(sk) ?
-                        dst_mtu(&rt->dst) : READ_ONCE(rt->dst.dev->mtu);
-
-       if (!inetdev_valid_mtu(cork->fragsize))
-               return -ENETUNREACH;
-
        cork->gso_size = ipc->gso_size;

        cork->dst = &rt->dst;