Fix possible double-free in pkcs7 add_attribute function

The problem is the ownership of the input parameter value
is transfered to the X509_ATTRIBUTE object attr, as soon
as X509_ATTRIBUTE_create succeeds, but when an error happens
after that point there is no way to get the ownership back
to the caller, which is necessary to fullfill the API contract.

Fixed that by moving the call to X509_ATTRIBUTE_create to the
end of the function, and make sure that no errors are possible
after that point.

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22721)

(cherry picked from commit 82a13a1f5053462f826bfb90061f0f77e3cc98a5)

diff --git a/crypto/pkcs7/pk7_doit.c b/crypto/pkcs7/pk7_doit.c
index 1cef67b211af775cbd3c33c588419c8d4c648b62..0d56e923de60d50487d738c3b86c372f7d694533 100644 (file)
--- a/crypto/pkcs7/pk7_doit.c
+++ b/crypto/pkcs7/pk7_doit.c
@@ -1239,36 +1239,29 @@ static int add_attribute(STACK_OF(X509_ATTRIBUTE) **sk, int nid, int atrtype,
                          void *value)
 {
     X509_ATTRIBUTE *attr = NULL;
+    int i, n;
 
     if (*sk == NULL) {
         if ((*sk = sk_X509_ATTRIBUTE_new_null()) == NULL)
             return 0;
- new_attrib:
-        if ((attr = X509_ATTRIBUTE_create(nid, atrtype, value)) == NULL)
-            return 0;
-        if (!sk_X509_ATTRIBUTE_push(*sk, attr)) {
-            X509_ATTRIBUTE_free(attr);
-            return 0;
-        }
-    } else {
-        int i;
-
-        for (i = 0; i < sk_X509_ATTRIBUTE_num(*sk); i++) {
-            attr = sk_X509_ATTRIBUTE_value(*sk, i);
-            if (OBJ_obj2nid(X509_ATTRIBUTE_get0_object(attr)) == nid) {
-                X509_ATTRIBUTE_free(attr);
-                attr = X509_ATTRIBUTE_create(nid, atrtype, value);
-                if (attr == NULL)
-                    return 0;
-                if (!sk_X509_ATTRIBUTE_set(*sk, i, attr)) {
-                    X509_ATTRIBUTE_free(attr);
-                    return 0;
-                }
-                goto end;
-            }
-        }
-        goto new_attrib;
     }
+    n = sk_X509_ATTRIBUTE_num(*sk);
+    for (i = 0; i < n; i++) {
+        attr = sk_X509_ATTRIBUTE_value(*sk, i);
+        if (OBJ_obj2nid(X509_ATTRIBUTE_get0_object(attr)) == nid)
+            goto end;
+    }
+    if (!sk_X509_ATTRIBUTE_push(*sk, NULL))
+        return 0;
+
  end:
+    attr = X509_ATTRIBUTE_create(nid, atrtype, value);
+    if (attr == NULL) {
+        if (i == n)
+            sk_X509_ATTRIBUTE_pop(*sk);
+        return 0;
+    }
+    X509_ATTRIBUTE_free(sk_X509_ATTRIBUTE_value(*sk, i));
+    (void) sk_X509_ATTRIBUTE_set(*sk, i, attr);
     return 1;
 }