Disable X509_STORE_CTX_purpose_inherit()

Nothing uses this function, except two internal callers. So split its guts
temporarily into a helper function and disable the gross general case.
The internal helper can be simplified by observing that def_purpose == 0:

Overriding 0 by 0 doesn't do anything, so drop that bit. Rename ptmp into
purp, and inline X509_PURPOSE_get_by_id(), i.e., make appropriate checks and
subtract X509_PURPOSE_MIN. The fallback to X509_PURPOSE_get_by_id(0) will
always fail since X509_PURPOSE_MIN == 1. So ditch that call. In particular,
X509_STORE_CTX_set_purpose(ctx, X509_PURPOSE_ANY) fails in current because
of this. That's nonsense. So remove the purp->trust == X509_TRUST_DEFAULT
check as only change of behavior. This matches what OpenSSL do nowadays.
They now set def_purpose = purpose if purpose != 0 and def_purpose == 0,
so in all real-world uses of this function they will just fetch the same
purpose again and do not check for default trust the second time around.
Finally, X509_TRUST_get_by_id() is only used to ensure that a non-zero (or
overridden) trust is between X509_TRUST_MIN and X509_TRUST_MAX. So expand
that into its explicit form.

ok jsing

1 files changed, 22 insertions, 23 deletions

diff --git a/src/lib/libcrypto/x509/x509_vfy.c b/src/lib/libcrypto/x509/x509_vfy.c
index 92aa9dfc5b..3d6b68afee 100644
--- a/src/lib/libcrypto/x509/x509_vfy.c
+++ b/src/lib/libcrypto/x509/x509_vfy.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: x509_vfy.c,v 1.136 2024/01/07 18:15:42 tb Exp $ */
+/* $OpenBSD: x509_vfy.c,v 1.137 2024/01/08 10:06:50 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -2177,35 +2177,35 @@ int
 X509_STORE_CTX_purpose_inherit(X509_STORE_CTX *ctx, int def_purpose,
     int purpose, int trust)
 {
-        int idx;
+        X509error(ERR_R_DISABLED);
+        return 0;
+}
+LCRYPTO_ALIAS(X509_STORE_CTX_purpose_inherit);
 
-        /* If purpose not set use default */
-        if (purpose == 0)
-                purpose = def_purpose;
+static int
+x509_vfy_purpose_inherit(X509_STORE_CTX *ctx, int purpose, int trust)
+{
         /* If we have a purpose then check it is valid */
         if (purpose != 0) {
-                X509_PURPOSE *ptmp;
-                idx = X509_PURPOSE_get_by_id(purpose);
-                if (idx == -1) {
+                const X509_PURPOSE *purp;
+                int purpose_idx;
+
+                if (purpose < X509_PURPOSE_MIN || purpose > X509_TRUST_MAX) {
                         X509error(X509_R_UNKNOWN_PURPOSE_ID);
                         return 0;
                 }
-                ptmp = X509_PURPOSE_get0(idx);
-                if (ptmp->trust == X509_TRUST_DEFAULT) {
-                        idx = X509_PURPOSE_get_by_id(def_purpose);
-                        if (idx == -1) {
-                                X509error(X509_R_UNKNOWN_PURPOSE_ID);
-                                return 0;
-                        }
-                        ptmp = X509_PURPOSE_get0(idx);
+                purpose_idx = purpose - X509_PURPOSE_MIN;
+                if ((purp = X509_PURPOSE_get0(purpose_idx)) == NULL) {
+                        X509error(X509_R_UNKNOWN_PURPOSE_ID);
+                        return 0;
                 }
-                /* If trust not set then get from purpose default */
+
+                /* If trust is unset, use the purpose's trust. */
                 if (trust == 0)
-                        trust = ptmp->trust;
+                        trust = purp->trust;
         }
         if (trust != 0) {
-                idx = X509_TRUST_get_by_id(trust);
-                if (idx == -1) {
+                if (trust < X509_TRUST_MIN || trust > X509_TRUST_MAX) {
                         X509error(X509_R_UNKNOWN_TRUST_ID);
                         return 0;
                 }
@@ -2218,19 +2218,18 @@ X509_STORE_CTX_purpose_inherit(X509_STORE_CTX *ctx, int def_purpose,
 
         return 1;
 }
-LCRYPTO_ALIAS(X509_STORE_CTX_purpose_inherit);
 
 int
 X509_STORE_CTX_set_purpose(X509_STORE_CTX *ctx, int purpose)
 {
-        return X509_STORE_CTX_purpose_inherit(ctx, 0, purpose, 0);
+        return x509_vfy_purpose_inherit(ctx, purpose, 0);
 }
 LCRYPTO_ALIAS(X509_STORE_CTX_set_purpose);
 
 int
 X509_STORE_CTX_set_trust(X509_STORE_CTX *ctx, int trust)
 {
-        return X509_STORE_CTX_purpose_inherit(ctx, 0, 0, trust);
+        return x509_vfy_purpose_inherit(ctx, 0, trust);
 }
 LCRYPTO_ALIAS(X509_STORE_CTX_set_trust);