Re: [PATCH] src: try SO_SNDBUF before SO_SNDBUFFORCE

[Pablo Neira Ayuso <pablo@netfilter.org>]

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Hi,

On Sun, Apr 09, 2023 at 01:09:07AM +0200, Pablo Neira Ayuso wrote:
> > diff --git a/src/mnl.c b/src/mnl.c
> > index 26f943db..ab6750c8 100644
> > --- a/src/mnl.c
> > +++ b/src/mnl.c
> > @@ -260,6 +260,13 @@ static void mnl_set_sndbuffer(const struct mnl_socket *nl,
> >  		return;
> >  
> >  	/* Rise sender buffer length to avoid hitting -EMSGSIZE */
> > +	if (setsockopt(mnl_socket_get_fd(nl), SOL_SOCKET, SO_SNDBUF,
> > +		       &newbuffsiz, sizeof(socklen_t)) == 0)
> > +		return;
> 
> setsockopt() with SO_SNDBUF never fails: it trims the newbuffsiz that is
> specified by net.core.wmem_max
> 
> This needs to call:
> 
> 	setsockopt(mnl_socket_get_fd(nl), SOL_SOCKET, SO_SNDBUF,
> 		   &newbuffsiz, sizeof(socklen_t));
> 
> without checking the return value. Otherwise, SO_SNDBUFFORCE is never
> going to be called after this patch. This needs a v2.

I think this patch should be fine.

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diff --git a/src/mnl.c b/src/mnl.c
index 26f943dbb4c8..ee62c0c9c2a0 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -261,8 +261,13 @@ static void mnl_set_sndbuffer(const struct mnl_socket *nl,
 
 	/* Rise sender buffer length to avoid hitting -EMSGSIZE */
 	if (setsockopt(mnl_socket_get_fd(nl), SOL_SOCKET, SO_SNDBUFFORCE,
-		       &newbuffsiz, sizeof(socklen_t)) < 0)
-		return;
+		       &newbuffsiz, sizeof(socklen_t)) < 0) {
+		/* Fall back to SO_SNDBUF, this never fails, kernel trims down
+		 * the size to net.core.wmem_max.
+		 */
+		setsockopt(mnl_socket_get_fd(nl), SOL_SOCKET, SO_SNDBUF,
+			   &newbuffsiz, sizeof(socklen_t));
+	}
 }
 
 static unsigned int nlsndbufsiz;