replace strstr() with strchr() for single characters

strstr() is used to match multiple characters in the haystack,
whereas strchr() is used to matched only single character.

CLA: trivial

Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #23347)

apps/engine.c

@@ -251,7 +251,7 @@ static void util_do_cmds(ENGINE *e, STACK_OF(OPENSSL_STRING) *cmds,
         cmd = sk_OPENSSL_STRING_value(cmds, loop);
         res = 1;                /* assume success */
         /* Check if this command has no ":arg" */
-        if ((arg = strstr(cmd, ":")) == NULL) {
+        if ((arg = strchr(cmd, ':')) == NULL) {
             if (!ENGINE_ctrl_cmd_string(e, cmd, NULL, 0))
                 res = 0;
         } else {

crypto/dso/dso_dl.c

@@ -217,7 +217,7 @@ static char *dl_name_converter(DSO *dso, const char *filename)
 
     len = strlen(filename);
     rsize = len + 1;
-    transform = (strstr(filename, "/") == NULL);
+    transform = (strchr(filename, '/') == NULL);
     if (transform) {
         /* We will convert this to "%s.s?" or "lib%s.s?" */
         rsize += strlen(DSO_EXTENSION); /* The length of ".s?" */

crypto/dso/dso_dlfcn.c

@@ -251,7 +251,7 @@ static char *dlfcn_name_converter(DSO *dso, const char *filename)
 
     len = strlen(filename);
     rsize = len + 1;
-    transform = (strstr(filename, "/") == NULL);
+    transform = (strchr(filename, '/') == NULL);
     if (transform) {
         /* We will convert this to "%s.so" or "lib%s.so" etc */
         rsize += strlen(DSO_EXTENSION);    /* The length of ".so" */

ssl/ssl_conf.c

@@ -241,7 +241,7 @@ static int cmd_ECDHParameters(SSL_CONF_CTX *cctx, const char *value)
         return 1;
 
     /* ECDHParameters accepts a single group name */
-    if (strstr(value, ":") != NULL)
+    if (strchr(value, ':') != NULL)
         return 0;
 
     if (cctx->ctx)