[PATCH v2] net/sctp: Make sha1 as default algorithm if fips is enabled

[Ashwin Dayanand Kamat <kashwindayan@vmware.com>]

MD5 is not FIPS compliant. But still md5 was used as the default
algorithm for sctp if fips was enabled.
Due to this, listen() system call in ltp tests was failing for sctp
in fips environment, with below error message.

[ 6397.892677] sctp: failed to load transform for md5: -2

Fix is to not assign md5 as default algorithm for sctp
if fips_enabled is true. Instead make sha1 as default algorithm.

Fixes: ltp testcase failure "cve-2018-5803 sctp_big_chunk"
Signed-off-by: Ashwin Dayanand Kamat <kashwindayan@vmware.com>
---
v2:
the listener can still fail if fips mode is enabled after
that the netns is initialized. So taking action in sctp_listen_start()
and buming a ratelimited notice the selected hmac is changed due to fips.
---
 net/sctp/socket.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index b91616f819de..a1107f42869e 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -49,6 +49,7 @@
 #include <linux/poll.h>
 #include <linux/init.h>
 #include <linux/slab.h>
+#include <linux/fips.h>
 #include <linux/file.h>
 #include <linux/compat.h>
 #include <linux/rhashtable.h>
@@ -8496,6 +8497,15 @@ static int sctp_listen_start(struct sock *sk, int backlog)
 	struct crypto_shash *tfm = NULL;
 	char alg[32];
 
+	if (fips_enabled && !strcmp(sp->sctp_hmac_alg, "md5")) {
+#if (IS_ENABLED(CONFIG_SCTP_DEFAULT_COOKIE_HMAC_SHA1))
+		sp->sctp_hmac_alg = "sha1";
+#else
+		sp->sctp_hmac_alg = NULL;
+#endif
+		net_info_ratelimited("changing the hmac algorithm, as md5 is not supported when fips is enabled");
+	}
+
 	/* Allocate HMAC for generating cookie. */
 	if (!sp->hmac && sp->sctp_hmac_alg) {
 		sprintf(alg, "hmac(%s)", sp->sctp_hmac_alg);
-- 
2.39.0