netlink: Use 8 KiB * netlink message header size as response buffer

...instead of BUFSIZ. On musl, BUFSIZ is 1024, so we'll typically
truncate the response to the request we send in nl_link(). It's
usually 8192 or more with glibc.

There doesn't seem to be any macro defining the rtnetlink maximum
message size, and iproute2 just hardcodes 1024 * 1024 for the receive
buffer, but the example in netlink(7) makes somewhat sense, looking
at the kernel implementation.

It's not very clean, but we're very unlikely to hit that limit,
and if we do, we'll find out painlessly, because NLA_OK() will tell
us right away.

Reported-by: Chris Kuhn <kuhnchris+passt@kuhnchris.eu>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 9 insertions, 6 deletions

diff --git a/netlink.c b/netlink.c
index 8f785ca..0e0be4f 100644
--- a/netlink.c
+++ b/netlink.c
@@ -34,6 +34,8 @@
 #include "log.h"
 #include "netlink.h"
 
+#define NLBUFSIZ	(8192 * sizeof(struct nlmsghdr)) /* See netlink(7) */
+
 /* Socket in init, in target namespace, sequence (just needs to be monotonic) */
 static int nl_sock	= -1;
 static int nl_sock_ns	= -1;
@@ -105,7 +107,7 @@ fail:
 static int nl_req(int ns, char *buf, const void *req, ssize_t len)
 {
 	int s = ns ? nl_sock_ns : nl_sock, done = 0;
-	char flush[BUFSIZ];
+	char flush[NLBUFSIZ];
 	ssize_t n;
 
 	while (!done && (n = recv(s, flush, sizeof(flush), MSG_DONTWAIT)) > 0) {
@@ -121,7 +123,8 @@ static int nl_req(int ns, char *buf, const void *req, ssize_t len)
 		}
 	}
 
-	if ((send(s, req, len, 0) < len) || (len = recv(s, buf, BUFSIZ, 0)) < 0)
+	if ((send(s, req, len, 0) < len) ||
+	    (len = recv(s, buf, NLBUFSIZ, 0)) < 0)
 		return -errno;
 
 	return len;
@@ -149,7 +152,7 @@ unsigned int nl_get_ext_if(sa_family_t af)
 	};
 	struct nlmsghdr *nh;
 	struct rtattr *rta;
-	char buf[BUFSIZ];
+	char buf[NLBUFSIZ];
 	ssize_t n;
 	size_t na;
 
@@ -227,7 +230,7 @@ void nl_route(int ns, unsigned int ifi, sa_family_t af, void *gw)
 	struct nlmsghdr *nh;
 	struct rtattr *rta;
 	struct rtmsg *rtm;
-	char buf[BUFSIZ];
+	char buf[NLBUFSIZ];
 	ssize_t n;
 	size_t na;
 
@@ -336,7 +339,7 @@ void nl_addr(int ns, unsigned int ifi, sa_family_t af,
 	struct ifaddrmsg *ifa;
 	struct nlmsghdr *nh;
 	struct rtattr *rta;
-	char buf[BUFSIZ];
+	char buf[NLBUFSIZ];
 	ssize_t n;
 	size_t na;
 
@@ -446,7 +449,7 @@ void nl_link(int ns, unsigned int ifi, void *mac, int up, int mtu)
 	struct ifinfomsg *ifm;
 	struct nlmsghdr *nh;
 	struct rtattr *rta;
-	char buf[BUFSIZ];
+	char buf[NLBUFSIZ];
 	ssize_t n;
 	size_t na;