net: sctp: propagate sysctl errors from proc_do* properly

[ Upstream commit ff5e92c1 ]

sysctl handler proc_sctp_do_hmac_alg(), proc_sctp_do_rto_min() and
proc_sctp_do_rto_max() do not properly reflect some error cases
when writing values via sysctl from internal proc functions such
as proc_dointvec() and proc_dostring().

In all these cases we pass the test for write != 0 and partially
do additional work just to notice that additional sanity checks
fail and we return with hard-coded -EINVAL while proc_do*
functions might also return different errors. So fix this up by
simply testing a successful return of proc_do* right after
calling it.

This also allows to propagate its return value onwards to the user.
While touching this, also fix up some minor style issues.

Fixes: 4f3fdf3b ("sctp: add check rto_min and rto_max in sysctl")
Fixes: 3c68198e ("sctp: Make hmac algorithm selection for cookie generation dynamic")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

net/sctp/sysctl.c

@@ -303,41 +303,40 @@ static int proc_sctp_do_hmac_alg(struct ctl_table *ctl,
 				loff_t *ppos)
 {
 	struct net *net = current->nsproxy->net_ns;
-	char tmp[8];
 	struct ctl_table tbl;
-	int ret;
-	int changed = 0;
+	bool changed = false;
 	char *none = "none";
+	char tmp[8];
+	int ret;
 
 	memset(&tbl, 0, sizeof(struct ctl_table));
 
 	if (write) {
 		tbl.data = tmp;
-		tbl.maxlen = 8;
+		tbl.maxlen = sizeof(tmp);
 	} else {
 		tbl.data = net->sctp.sctp_hmac_alg ? : none;
 		tbl.maxlen = strlen(tbl.data);
 	}
-		ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
 
-	if (write) {
+	ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
+	if (write && ret == 0) {
 #ifdef CONFIG_CRYPTO_MD5
 		if (!strncmp(tmp, "md5", 3)) {
 			net->sctp.sctp_hmac_alg = "md5";
-			changed = 1;
+			changed = true;
 		}
 #endif
 #ifdef CONFIG_CRYPTO_SHA1
 		if (!strncmp(tmp, "sha1", 4)) {
 			net->sctp.sctp_hmac_alg = "sha1";
-			changed = 1;
+			changed = true;
 		}
 #endif
 		if (!strncmp(tmp, "none", 4)) {
 			net->sctp.sctp_hmac_alg = NULL;
-			changed = 1;
+			changed = true;
 		}
-
 		if (!changed)
 			ret = -EINVAL;
 	}