Rewrite X509V3_get_d2i()

This API is wrapped by nine *_get{,1}_ext_d2i() functions and they all
have the same defect: if an idx variable is passed in, multiple extensions
are handled incorrectly.

Clean up the mess that was the current implementation by replacing the
reimplementation of X509v3_get_ext_by_NID() with extra twists by actual
calls to the real thing. This way the madness is implemented explicitly
and can be explained in comments. The code still gets shorter.

In brief: always call this API with a known nid, pass crit, and a NULL idx.
If NULL is returned, crit != -1 is an error (malformed cert or allocation
failure).

ok jsing

1 files changed, 47 insertions, 56 deletions

diff --git a/src/lib/libcrypto/x509/x509_lib.c b/src/lib/libcrypto/x509/x509_lib.c
index 4347875885..161e638427 100644
--- a/src/lib/libcrypto/x509/x509_lib.c
+++ b/src/lib/libcrypto/x509/x509_lib.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: x509_lib.c,v 1.21 2024/05/28 15:40:38 tb Exp $ */
+/* $OpenBSD: x509_lib.c,v 1.22 2024/06/17 05:31:26 tb Exp $ */
 /* Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL
  * project 1999.
  */
@@ -178,69 +178,60 @@ X509V3_EXT_d2i(X509_EXTENSION *ext)
 }
 LCRYPTO_ALIAS(X509V3_EXT_d2i);
 
-/* Get critical flag and decoded version of extension from a NID.
- * The "idx" variable returns the last found extension and can
- * be used to retrieve multiple extensions of the same NID.
- * However multiple extensions with the same NID is usually
- * due to a badly encoded certificate so if idx is NULL we
- * choke if multiple extensions exist.
- * The "crit" variable is set to the critical value.
- * The return value is the decoded extension or NULL on
- * error. The actual error can have several different causes,
- * the value of *crit reflects the cause:
- * >= 0, extension found but not decoded (reflects critical value).
- * -1 extension not found.
- * -2 extension occurs more than once.
+/*
+ * This API is only safe to call with known nid, crit != NULL and idx == NULL.
+ * On NULL return, crit acts as a failure indicator: crit == -1 means an
+ * extension of type nid was not present, crit != -1 is fatal: crit == -2
+ * means multiple extensions of type nid are present; if crit is 0 or 1, this
+ * implies the extension was found but could not be decoded.
  */
 
 void *
 X509V3_get_d2i(const STACK_OF(X509_EXTENSION) *x, int nid, int *crit, int *idx)
 {
-        int lastpos, i;
-        X509_EXTENSION *ex, *found_ex = NULL;
-
-        if (!x) {
-                if (idx)
-                        *idx = -1;
-                if (crit)
-                        *crit = -1;
+        X509_EXTENSION *ext;
+        int lastpos = idx == NULL ? -1 : *idx;
+
+        if (crit != NULL)
+                *crit = -1;
+        if (idx != NULL)
+                *idx = -1;
+
+        /*
+         * Nothing to do if no extensions, unknown nid, or missing extension.
+         */
+
+        if (x == NULL)
+                return NULL;
+        if ((lastpos = X509v3_get_ext_by_NID(x, nid, lastpos)) < 0)
+                return NULL;
+        if ((ext = X509v3_get_ext(x, lastpos)) == NULL)
+                return NULL;
+
+        /*
+         * API madness. Only check for a second extension of type nid if
+         * idx == NULL. Indicate this by setting *crit to -2. If idx != NULL,
+         * don't care and set *idx to the index of the first extension found.
+         */
+
+        if (idx == NULL && X509v3_get_ext_by_NID(x, nid, lastpos) > 0) {
+                if (crit != NULL)
+                        *crit = -2;
                 return NULL;
-        }
-        if (idx)
-                lastpos = *idx + 1;
-        else
-                lastpos = 0;
-        if (lastpos < 0)
-                lastpos = 0;
-        for (i = lastpos; i < sk_X509_EXTENSION_num(x); i++) {
-                ex = sk_X509_EXTENSION_value(x, i);
-                if (OBJ_obj2nid(ex->object) == nid) {
-                        if (idx) {
-                                *idx = i;
-                                found_ex = ex;
-                                break;
-                        } else if (found_ex) {
-                                /* Found more than one */
-                                if (crit)
-                                        *crit = -2;
-                                return NULL;
-                        }
-                        found_ex = ex;
-                }
-        }
-        if (found_ex) {
-                /* Found it */
-                if (crit)
-                        *crit = X509_EXTENSION_get_critical(found_ex);
-                return X509V3_EXT_d2i(found_ex);
         }
 
-        /* Extension not found */
-        if (idx)
-                *idx = -1;
-        if (crit)
-                *crit = -1;
-        return NULL;
+        /*
+         * Another beautiful API detail: *crit will be set to 0 or 1, so if the
+         * extension fails to decode, we can deduce this from return value NULL
+         * and crit != -1.
+         */
+
+        if (crit != NULL)
+                *crit = X509_EXTENSION_get_critical(ext);
+        if (idx != NULL)
+                *idx = lastpos;
+
+        return X509V3_EXT_d2i(ext);
 }
 LCRYPTO_ALIAS(X509V3_get_d2i);