[PATCH net-next v3 5/5] sctp: Stop accepting md5 and sha1 for net.sctp.cookie_hmac_alg

[Eric Biggers <ebiggers@kernel.org>]

The upgrade of the cookie authentication algorithm to HMAC-SHA256 kept
some backwards compatibility for the net.sctp.cookie_hmac_alg sysctl by
still accepting the values 'md5' and 'sha1'.  Those algorithms are no
longer actually used, but rather those values were just treated as
requests to enable cookie authentication.

As requested at
https://lore.kernel.org/netdev/CADvbK_fmCRARc8VznH8cQa-QKaCOQZ6yFbF=1-VDK=zRqv_cXw@mail.gmail.com/
and https://lore.kernel.org/netdev/20250818084345.708ac796@kernel.org/ ,
go further and start rejecting 'md5' and 'sha1' completely.

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---
 Documentation/networking/ip-sysctl.rst | 3 ---
 net/sctp/sysctl.c                      | 4 +---
 2 files changed, 1 insertion(+), 6 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 3d6782683eee7..43badb338d22b 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -3509,13 +3509,10 @@ cookie_hmac_alg - STRING
 	Valid values are:
 
 	* sha256
 	* none
 
-	md5 and sha1 are also accepted for backwards compatibility, but cause
-	sha256 to be selected.
-
 	Default: sha256
 
 rcvbuf_policy - INTEGER
 	Determines if the receive buffer is attributed to the socket or to
 	association.   SCTP supports the capability to create multiple
diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c
index 19acc57c3ed97..15e7db9a3ab2e 100644
--- a/net/sctp/sysctl.c
+++ b/net/sctp/sysctl.c
@@ -399,13 +399,11 @@ static int proc_sctp_do_hmac_alg(const struct ctl_table *ctl, int write,
 		tbl.data = tmp;
 		tbl.maxlen = sizeof(tmp) - 1;
 		ret = proc_dostring(&tbl, 1, buffer, lenp, ppos);
 		if (ret)
 			return ret;
-		if (!strcmp(tmp, "sha256") ||
-		    /* for backwards compatibility */
-		    !strcmp(tmp, "md5") || !strcmp(tmp, "sha1")) {
+		if (!strcmp(tmp, "sha256")) {
 			net->sctp.cookie_auth_enable = 1;
 			return 0;
 		}
 		if (!strcmp(tmp, "none")) {
 			net->sctp.cookie_auth_enable = 0;
-- 
2.50.1