sctp: Make hmac algorithm selection for cookie generation dynamic

Currently sctp allows for the optional use of md5 of sha1 hmac algorithms to
generate cookie values when establishing new connections via two build time
config options.  Theres no real reason to make this a static selection.  We can
add a sysctl that allows for the dynamic selection of these algorithms at run
time, with the default value determined by the corresponding crypto library
availability.
This comes in handy when, for example running a system in FIPS mode, where use
of md5 is disallowed, but SHA1 is permitted.

Note: This new sysctl has no corresponding socket option to select the cookie
hmac algorithm.  I chose not to implement that intentionally, as RFC 6458
contains no option for this value, and I opted not to pollute the socket option
namespace.

Change notes:
v2)
	* Updated subject to have the proper sctp prefix as per Dave M.
	* Replaced deafult selection options with new options that allow
	  developers to explicitly select available hmac algs at build time
	  as per suggestion by Vlad Y.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Vlad Yasevich <vyasevich@gmail.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: netdev@vger.kernel.org
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 59 insertions, 0 deletions

diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c
index 70e3ba5cb50b..043889ac86c0 100644
--- a/net/sctp/sysctl.c
+++ b/net/sctp/sysctl.c
@@ -62,6 +62,11 @@ extern long sysctl_sctp_mem[3];
 extern int sysctl_sctp_rmem[3];
 extern int sysctl_sctp_wmem[3];
 
+static int proc_sctp_do_hmac_alg(ctl_table *ctl,
+				int write,
+				void __user *buffer, size_t *lenp,
+
+				loff_t *ppos);
 static ctl_table sctp_table[] = {
 	{
 		.procname	= "sctp_mem",
@@ -147,6 +152,12 @@ static ctl_table sctp_net_table[] = {
 		.proc_handler	= proc_dointvec,
 	},
 	{
+		.procname	= "cookie_hmac_alg",
+		.maxlen		= 8,
+		.mode		= 0644,
+		.proc_handler	= proc_sctp_do_hmac_alg,
+	},
+	{
 		.procname	= "valid_cookie_life",
 		.data		= &init_net.sctp.valid_cookie_life,
 		.maxlen		= sizeof(unsigned int),
@@ -289,6 +300,54 @@ static ctl_table sctp_net_table[] = {
 	{ /* sentinel */ }
 };
 
+static int proc_sctp_do_hmac_alg(ctl_table *ctl,
+				int write,
+				void __user *buffer, size_t *lenp,
+				loff_t *ppos)
+{
+	struct net *net = current->nsproxy->net_ns;
+	char tmp[8];
+	ctl_table tbl;
+	int ret;
+	int changed = 0;
+	char *none = "none";
+
+	memset(&tbl, 0, sizeof(struct ctl_table));
+
+	if (write) {
+		tbl.data = tmp;
+		tbl.maxlen = 8;
+	} else {
+		tbl.data = net->sctp.sctp_hmac_alg ? : none;
+		tbl.maxlen = strlen(tbl.data);
+	}
+		ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
+
+	if (write) {
+#ifdef CONFIG_CRYPTO_MD5
+		if (!strncmp(tmp, "md5", 3)) {
+			net->sctp.sctp_hmac_alg = "md5";
+			changed = 1;
+		}
+#endif
+#ifdef CONFIG_CRYPTO_SHA1
+		if (!strncmp(tmp, "sha1", 4)) {
+			net->sctp.sctp_hmac_alg = "sha1";
+			changed = 1;
+		}
+#endif
+		if (!strncmp(tmp, "none", 4)) {
+			net->sctp.sctp_hmac_alg = NULL;
+			changed = 1;
+		}
+
+		if (!changed)
+			ret = -EINVAL;
+	}
+
+	return ret;
+}
+
 int sctp_sysctl_net_register(struct net *net)
 {
 	struct ctl_table *table;