From 5214d7e59fe4d5d89e14e8e7b654ded25f918afb Mon Sep 17 00:00:00 2001
From: Ondrej Zajicek <santiago@crfreenet.org>
Date: Thu, 1 Aug 2024 14:55:05 +0200
Subject: [PATCH] IO: Ensure that socket rcvbuf is large enough

The socket structure has the field rbsize (receive buffer size), which
controls the size of the userspace receive buffer. There is also kernel
receive buffer, which in some cases may be smaller (e.g. on FreeBSD it
is by default ~8k). The patch ensures that the kernel receive buffer is
as large as the userspace receive buffer.
---
 sysdep/unix/io.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/sysdep/unix/io.c b/sysdep/unix/io.c
index 987c7a6b..59b33ef1 100644
--- a/sysdep/unix/io.c
+++ b/sysdep/unix/io.c
@@ -517,6 +517,40 @@ sk_set_high_port(sock *s UNUSED)
   return 0;
 }
 
+static inline int
+sk_set_min_rcvbuf_(sock *s, int bufsize)
+{
+  int oldsize = 0, oldsize_s = sizeof(oldsize);
+
+  if (getsockopt(s->fd, SOL_SOCKET, SO_RCVBUF, &oldsize, &oldsize_s) < 0)
+    ERR("SO_RCVBUF");
+
+  if (oldsize >= bufsize)
+    return 0;
+
+  bufsize = BIRD_ALIGN(bufsize, 64);
+  if (setsockopt(s->fd, SOL_SOCKET, SO_RCVBUF, &bufsize, sizeof(bufsize)) < 0)
+    ERR("SO_RCVBUF");
+
+  /*
+  int newsize = 0, newsize_s = sizeof(newsize);
+  if (getsockopt(s->fd, SOL_SOCKET, SO_RCVBUF, &newsize, &newsize_s) < 0)
+    ERR("SO_RCVBUF");
+
+  log(L_INFO "Setting rcvbuf on %s from %d to %d",
+      s->iface ? s->iface->name : "*", oldsize, newsize);
+  */
+
+  return 0;
+}
+
+static void
+sk_set_min_rcvbuf(sock *s, int bufsize)
+{
+  if (sk_set_min_rcvbuf_(s, bufsize) < 0)
+    log(L_WARN "Socket error: %s%#m", s->err);
+}
+
 static inline byte *
 sk_skip_ip_header(byte *pkt, int *len)
 {
@@ -862,6 +896,9 @@ sk_set_rbsize(sock *s, uint val)
   xfree(s->rbuf_alloc);
   s->rbuf_alloc = xmalloc(val);
   s->rpos = s->rbuf = s->rbuf_alloc;
+
+  if ((s->type == SK_UDP) || (s->type == SK_IP))
+    sk_set_min_rcvbuf(s, s->rbsize);
 }
 
 void
@@ -1058,6 +1095,9 @@ sk_setup(sock *s)
     if (sk_set_priority(s, s->priority) < 0)
       return -1;
 
+  if ((s->type == SK_UDP) || (s->type == SK_IP))
+    sk_set_min_rcvbuf(s, s->rbsize);
+
   return 0;
 }