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>

2 files changed, 1 insertions, 8 deletions

diff --git a/include/net/sctp/constants.h b/include/net/sctp/constants.h
index d053d2e..c29707d 100644
--- a/include/net/sctp/constants.h
+++ b/include/net/sctp/constants.h
@@ -312,14 +312,6 @@ enum { SCTP_MAX_GABS = 16 };
 				 * functions simpler to write.
 				 */
 
-#if defined (CONFIG_SCTP_HMAC_MD5)
-#define SCTP_COOKIE_HMAC_ALG "hmac(md5)"
-#elif defined (CONFIG_SCTP_HMAC_SHA1)
-#define SCTP_COOKIE_HMAC_ALG "hmac(sha1)"
-#else
-#define SCTP_COOKIE_HMAC_ALG NULL
-#endif
-
 /* These return values describe the success or failure of a number of
  * routines which form the lower interface to SCTP_outqueue.
  */
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 64158aa..2b2f61d 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -177,6 +177,7 @@ struct sctp_sock {
 
 	/* Access to HMAC transform. */
 	struct crypto_hash *hmac;
+	char *sctp_hmac_alg;
 
 	/* What is our base endpointer? */
 	struct sctp_endpoint *ep;