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, 13 insertions, 26 deletions

diff --git a/net/sctp/Kconfig b/net/sctp/Kconfig
index 126b014eb79b..a9edd2e205f4 100644
--- a/net/sctp/Kconfig
+++ b/net/sctp/Kconfig
@@ -9,7 +9,6 @@ menuconfig IP_SCTP
         select CRYPTO
         select CRYPTO_HMAC
         select CRYPTO_SHA1
-        select CRYPTO_MD5 if SCTP_HMAC_MD5
         select LIBCRC32C
         ---help---
           Stream Control Transmission Protocol
@@ -68,33 +67,21 @@ config SCTP_DBG_OBJCNT
 
           If unsure, say N
 
-choice
-        prompt "SCTP: Cookie HMAC Algorithm"
-        default SCTP_HMAC_MD5
+config SCTP_COOKIE_HMAC_MD5
+        bool "Enable optional MD5 hmac cookie generation"
         help
-          HMAC algorithm to be used during association initialization.  It
-          is strongly recommended to use HMAC-SHA1 or HMAC-MD5.  See 
-          configuration for Cryptographic API and enable those algorithms
-          to make usable by SCTP. 
-
-config SCTP_HMAC_NONE
-        bool "None"
-        help 
-          Choosing this disables the use of an HMAC during association 
-          establishment.  It is advised to use either HMAC-MD5 or HMAC-SHA1.
-
-config SCTP_HMAC_SHA1
-        bool "HMAC-SHA1"
-        help 
-          Enable the use of HMAC-SHA1 during association establishment.  It 
-          is advised to use either HMAC-MD5 or HMAC-SHA1.
-
-config SCTP_HMAC_MD5
-        bool "HMAC-MD5"
+          Enable optional MD5 hmac based SCTP cookie generation
+        default y
+        select CRYPTO_HMAC if SCTP_COOKIE_HMAC_MD5
+        select CRYPTO_MD5 if SCTP_COOKIE_HMAC_MD5
+
+config SCTP_COOKIE_HMAC_SHA1
+        bool "Enable optional SHA1 hmac cookie generation"
         help
-          Enable the use of HMAC-MD5 during association establishment.  It is 
-          advised to use either HMAC-MD5 or HMAC-SHA1.
+          Enable optional SHA1 hmac based SCTP cookie generation
+        default y
+        select CRYPTO_HMAC if SCTP_COOKIE_HMAC_SHA1
+        select CRYPTO_SHA1 if SCTP_COOKIE_HMAC_SHA1
 
-endchoice
 
 endif # IP_SCTP