netdev - Re: [PATCH v2] ipv6/sit: fix ipip6_tunnel_get

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Date:   Mon, 27 Jun 2022 11:01:07 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     zys.zljxml@...il.com
Cc:     LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Paolo Abeni <pabeni@...hat.com>,
        katrinzhou <katrinzhou@...cent.com>
Subject: Re: [PATCH v2] ipv6/sit: fix ipip6_tunnel_get_prl when memory
 allocation fails

On Sat, Jun 25, 2022 at 7:45 AM <zys.zljxml@...il.com> wrote:
>
> From: katrinzhou <katrinzhou@...cent.com>
>
> Fix an illegal copy_to_user() attempt when the system fails to
> allocate memory for prl due to a lack of memory.

I do not really see an illegal copy_to_user()

c = 0
-> len = 0

if ((len && copy_to_user(a + 1, kp, len)) || put_user(len, &a->datalen))

So the copy_to_user() should not be called ?

I think you should only mention that after this patch, correct error
code is returned (-ENOMEM)


>
> Addresses-Coverity: ("Unused value")
> Fixes: 300aaeeaab5f ("[IPV6] SIT: Add SIOCGETPRL ioctl to get/dump PRL.")
> Signed-off-by: katrinzhou <katrinzhou@...cent.com>
> ---
>
> Changes in v2:
> - Move the position of label "out"
>
>  net/ipv6/sit.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
> index c0b138c20992..3330882c0f94 100644
> --- a/net/ipv6/sit.c
> +++ b/net/ipv6/sit.c
> @@ -323,8 +323,6 @@ static int ipip6_tunnel_get_prl(struct net_device *dev, struct ip_tunnel_prl __u
>                 kcalloc(cmax, sizeof(*kp), GFP_KERNEL_ACCOUNT | __GFP_NOWARN) :
>                 NULL;
>
> -       rcu_read_lock();
> -
>         ca = min(t->prl_count, cmax);
>
>         if (!kp) {
> @@ -342,6 +340,7 @@ static int ipip6_tunnel_get_prl(struct net_device *dev, struct ip_tunnel_prl __u
>         }
>
>         c = 0;
> +       rcu_read_lock();
>         for_each_prl_rcu(t->prl) {
>                 if (c >= cmax)
>                         break;
> @@ -353,7 +352,7 @@ static int ipip6_tunnel_get_prl(struct net_device *dev, struct ip_tunnel_prl __u
>                 if (kprl.addr != htonl(INADDR_ANY))
>                         break;
>         }
> -out:
> +
>         rcu_read_unlock();
>
>         len = sizeof(*kp) * c;
> @@ -362,7 +361,7 @@ static int ipip6_tunnel_get_prl(struct net_device *dev, struct ip_tunnel_prl __u
>                 ret = -EFAULT;
>
>         kfree(kp);
> -
> +out:
>         return ret;
>  }
>
> --
> 2.27.0
>