"Stream" valid PKCS7 objects with omitted content

The PKCS#7 standard marks the content element of the ContentInfo OPTIONAL.
Accordingly, a PKCS#7 object only containing a Content Type OID is valid:

  SEQUENCE {
    OBJECT_IDENTIFIER { 1.2.840.113549.1.7.4 }
  }

Deserializing such an object works and therefore streaming should at least
have the decency of not segfaulting. Of course there's nothing decent about
PKCS#7 be it the standard or its OpenSSL "implementation".

Exercises a problem reported by Acts1361 and currently crashes.
To be fixed in pk7_lib.c r1.32.

1 files changed, 104 insertions, 4 deletions

diff --git a/src/regress/lib/libcrypto/pkcs7/pkcs7test.c b/src/regress/lib/libcrypto/pkcs7/pkcs7test.c
index 88126ea082..ae7c41299b 100644
--- a/src/regress/lib/libcrypto/pkcs7/pkcs7test.c
+++ b/src/regress/lib/libcrypto/pkcs7/pkcs7test.c
@@ -1,6 +1,7 @@
-/*      $OpenBSD: pkcs7test.c,v 1.6 2026/04/21 05:18:35 tb Exp $        */
+/*      $OpenBSD: pkcs7test.c,v 1.7 2026/08/30 16:52:07 tb Exp $        */
 /*
  * Copyright (c) 2014 Joel Sing <jsing@openbsd.org>
+ * Copyright (c) 2026 Theo Buehler <tb@openbsd.org>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -16,13 +17,16 @@
  */
 
 #include <err.h>
+#include <stdarg.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <unistd.h>
 
+#include <openssl/asn1.h>
 #include <openssl/bio.h>
 #include <openssl/err.h>
 #include <openssl/evp.h>
+#include <openssl/objects.h>
 #include <openssl/pem.h>
 #include <openssl/pkcs7.h>
 #include <openssl/x509.h>
@@ -100,9 +104,13 @@ x509_store_callback(int ok, X509_STORE_CTX *ctx)
 }
 
 static void
-fatal(const char *msg)
+fatal(const char *msg, ...)
 {
-        warnx("%s", msg);
+        va_list ap;
+
+        va_start(ap, msg);
+        vwarnx("%s", ap);
+        va_end(ap);
         ERR_print_errors_fp(stderr);
         exit(1);
 }
@@ -300,12 +308,104 @@ pkcs7_basics(void)
         return 0;
 }
 
+static int
+pkcs7_stream_missing_content_nid(int nid)
+{
+        PKCS7 *p7 = NULL;
+        const unsigned char *p, *name;
+        unsigned char **boundary = NULL;
+        unsigned char *der = NULL;
+        int der_len = 0;
+        int ret;
+        int failed = 1;
+
+        name = OBJ_nid2sn(nid);
+
+        /*
+         * Create PKCS7 object with Content Type corresponding to nid
+         * and omit the optional content.
+         */
+
+        if ((p7 = PKCS7_new()) == NULL)
+                fatal("PKCS7_new NID %d (%s)", nid, name);
+        ASN1_OBJECT_free(p7->type);
+        if ((p7->type = OBJ_nid2obj(nid)) == NULL)
+                fatal("OBJ_nid2obj NID %d (%s)", nid, name);
+
+        /*
+         * Round trip this through DER.
+         */
+
+        if ((der_len = i2d_PKCS7(p7, &der)) <= 0)
+                fatal("i2d_PKCS7 NID %d (%s)", nid, name);
+
+        PKCS7_free(p7);
+        p7 = NULL;
+
+        p = der;
+        if ((p7 = d2i_PKCS7(NULL, &p, der_len)) == NULL)
+                fatal("d2i_PKCS7 NID %d (%s)", nid, name);
+
+        /*
+         * It deserialized, so we can safely stream it, right?
+         */
+
+        if ((ret = PKCS7_stream(&boundary, p7)) != 0) {
+                fprintf(stderr, "FAILURE: PKCS7_stream for NID %d (%s) "
+                    "want 0, got %d\n", nid, name, ret);
+                goto out;
+        }
+
+        failed = 0;
+
+ out:
+        PKCS7_free(p7);
+        freezero(der, der_len);
+
+        return failed;
+}
+
+/*
+ * For each Content Type OID (RFC 2315, section 14), create a PKCS7 object that
+ * d2i_PKCS7() accepts. For x in [1..6] we use an object that encodes to
+ *
+ * SEQUENCE {
+ *   OBJECT_IDENTIFIER { 1.2.840.113549.1.7.x }
+ * }
+ *
+ * This works because RFC 2315 section 7 marks the content optional:
+ *
+ *  ContentInfo ::= SEQUENCE {
+ *    contentType ContentType,
+ *    content
+ *      [0] EXPLICIT ANY DEFINED BY contentType OPTIONAL }
+ *
+ * reflected in the ASN1_TFLG_OPTIONAL in pk7_asn1.c's p7default_tt.
+ */
+
+static int
+pkcs7_stream_missing_content(void)
+{
+        int failed = 0;
+
+        /* NID naming consistency is king. */
+        failed |= pkcs7_stream_missing_content_nid(NID_pkcs7_data);
+        failed |= pkcs7_stream_missing_content_nid(NID_pkcs7_signed);
+        failed |= pkcs7_stream_missing_content_nid(NID_pkcs7_enveloped);
+        failed |= pkcs7_stream_missing_content_nid(NID_pkcs7_signedAndEnveloped);
+        failed |= pkcs7_stream_missing_content_nid(NID_pkcs7_digest);
+        failed |= pkcs7_stream_missing_content_nid(NID_pkcs7_encrypted);
+
+        return failed;
+}
+
 int
 main(int argc, char **argv)
 {
         int failed = 0;
 
         failed |= pkcs7_basics();
+        failed |= pkcs7_stream_missing_content();
 
         return failed;
 }