[PATCH net-next v2] net: mctp: take ownership of skb in mctp_local_output

[PATCH net-next v2] net: mctp: take ownership of skb in mctp_local_output

[Jeremy Kerr]

Currently, mctp_local_output only takes ownership of skb on success, and
we may leak an skb if mctp_local_output fails in specific states; the
skb ownership isn't transferred until the actual output routing occurs.

Instead, make mctp_local_output free the skb on all error paths up to
the route action, so it always consumes the passed skb.

Fixes: 833ef3b91de6 ("mctp: Populate socket implementation")
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>

---
v2:
 - retain EINVAL return code in !rt && !ifindex case. Based on feedback
   from Simon Horman <horms@kernel.org>.
---
 include/net/mctp.h |  1 +
 net/mctp/route.c   | 10 ++++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/net/mctp.h b/include/net/mctp.h
index da86e106c91d..2bff5f47ce82 100644
--- a/include/net/mctp.h
+++ b/include/net/mctp.h
@@ -249,6 +249,7 @@ struct mctp_route {
 struct mctp_route *mctp_route_lookup(struct net *net, unsigned int dnet,
 				     mctp_eid_t daddr);
 
+/* always takes ownership of skb */
 int mctp_local_output(struct sock *sk, struct mctp_route *rt,
 		      struct sk_buff *skb, mctp_eid_t daddr, u8 req_tag);
 
diff --git a/net/mctp/route.c b/net/mctp/route.c
index 7a47a58aa54b..d0c43812bec3 100644
--- a/net/mctp/route.c
+++ b/net/mctp/route.c
@@ -888,7 +888,7 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
 		dev = dev_get_by_index_rcu(sock_net(sk), cb->ifindex);
 		if (!dev) {
 			rcu_read_unlock();
-			return rc;
+			goto out_free;
 		}
 		rt->dev = __mctp_dev_get(dev);
 		rcu_read_unlock();
@@ -903,7 +903,8 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
 		rt->mtu = 0;
 
 	} else {
-		return -EINVAL;
+		rc = -EINVAL;
+		goto out_free;
 	}
 
 	spin_lock_irqsave(&rt->dev->addrs_lock, flags);
@@ -966,12 +967,17 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
 		rc = mctp_do_fragment_route(rt, skb, mtu, tag);
 	}
 
+	/* route output functions consume the skb, even on error */
+	skb = NULL;
+
 out_release:
 	if (!ext_rt)
 		mctp_route_release(rt);
 
 	mctp_dev_put(tmp_rt.dev);
 
+out_free:
+	kfree_skb(skb);
 	return rc;
 }
 
-- 
2.39.2

Re: [PATCH net-next v2] net: mctp: take ownership of skb in mctp_local_output

[Simon Horman]

On Tue, Feb 20, 2024 at 04:10:53PM +0800, Jeremy Kerr wrote:
> Currently, mctp_local_output only takes ownership of skb on success, and
> we may leak an skb if mctp_local_output fails in specific states; the
> skb ownership isn't transferred until the actual output routing occurs.
> 
> Instead, make mctp_local_output free the skb on all error paths up to
> the route action, so it always consumes the passed skb.
> 
> Fixes: 833ef3b91de6 ("mctp: Populate socket implementation")
> Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
> 
> ---
> v2:
>  - retain EINVAL return code in !rt && !ifindex case. Based on feedback
>    from Simon Horman <horms@kernel.org>.

Hi Jeremy,

Thanks for the update.
This one looks good to me.

Reviewed-by: Simon Horman <horms@kernel.org>

Re: [PATCH net-next v2] net: mctp: take ownership of skb in mctp_local_output

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 20 Feb 2024 16:10:53 +0800 you wrote:
> Currently, mctp_local_output only takes ownership of skb on success, and
> we may leak an skb if mctp_local_output fails in specific states; the
> skb ownership isn't transferred until the actual output routing occurs.
> 
> Instead, make mctp_local_output free the skb on all error paths up to
> the route action, so it always consumes the passed skb.
> 
> [...]

Here is the summary with links:
  - [net-next,v2] net: mctp: take ownership of skb in mctp_local_output
    https://git.kernel.org/netdev/net/c/3773d65ae515

You are awesome, thank you!
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