[PATCH v8 10/27] mbedtls/external: support decoding multiple signer's cert

[Raymond Mao]

Support decoding multiple signer's cert in the signed data within
a PKCS7 message.

The PR for this patch is at:
https://github.com/Mbed-TLS/mbedtls/pull/9001

For enabling EFI loader PKCS7 features with MbedTLS build,
we need this patch on top of MbedTLS v3.6.0 before it is merged into
the next MbedTLS LTS release.

Signed-off-by: Raymond Mao <raymond.mao at linaro.org>
---
Changes in v2
- None.
Changes in v3
- Update commit message.
Changes in v4
- None.
Changes in v5
- None.
Changes in v6
- None.
Changes in v7
- None.
Changes in v8
- None

 lib/mbedtls/external/mbedtls/library/pkcs7.c | 75 ++++++++++++--------
 1 file changed, 47 insertions(+), 28 deletions(-)

diff --git a/lib/mbedtls/external/mbedtls/library/pkcs7.c b/lib/mbedtls/external/mbedtls/library/pkcs7.c
index da73fb341d6..01105227d7a 100644
--- a/lib/mbedtls/external/mbedtls/library/pkcs7.c
+++ b/lib/mbedtls/external/mbedtls/library/pkcs7.c
@@ -61,6 +61,36 @@ static int pkcs7_get_next_content_len(unsigned char **p, unsigned char *end,
     return ret;
 }
 
+/**
+ * Get and decode one cert from a sequence.
+ * Return 0 for success,
+ * Return negative error code for failure.
+ **/
+static int pkcs7_get_one_cert(unsigned char **p, unsigned char *end,
+                              mbedtls_x509_crt *certs)
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    size_t len = 0;
+    unsigned char *start = *p;
+    unsigned char *end_cert;
+
+    ret = mbedtls_asn1_get_tag(p, end, &len, MBEDTLS_ASN1_CONSTRUCTED
+                               | MBEDTLS_ASN1_SEQUENCE);
+    if (ret != 0) {
+        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_PKCS7_INVALID_CERT, ret);
+    }
+
+    end_cert = *p + len;
+
+    if ((ret = mbedtls_x509_crt_parse_der(certs, start, end_cert - start)) < 0) {
+        return MBEDTLS_ERR_PKCS7_INVALID_CERT;
+    }
+
+    *p = end_cert;
+
+    return 0;
+}
+
 /**
  * version Version
  * Version ::= INTEGER
@@ -178,11 +208,12 @@ static int pkcs7_get_certificates(unsigned char **p, unsigned char *end,
                                   mbedtls_x509_crt *certs)
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    size_t len1 = 0;
-    size_t len2 = 0;
-    unsigned char *end_set, *end_cert, *start;
+    size_t len = 0;
+    unsigned char *end_set;
+    int num_of_certs = 0;
 
-    ret = mbedtls_asn1_get_tag(p, end, &len1, MBEDTLS_ASN1_CONSTRUCTED
+    /* Get the set of certs */
+    ret = mbedtls_asn1_get_tag(p, end, &len, MBEDTLS_ASN1_CONSTRUCTED
                                | MBEDTLS_ASN1_CONTEXT_SPECIFIC);
     if (ret == MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
         return 0;
@@ -190,38 +221,26 @@ static int pkcs7_get_certificates(unsigned char **p, unsigned char *end,
     if (ret != 0) {
         return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_PKCS7_INVALID_FORMAT, ret);
     }
-    start = *p;
-    end_set = *p + len1;
+    end_set = *p + len;
 
-    ret = mbedtls_asn1_get_tag(p, end_set, &len2, MBEDTLS_ASN1_CONSTRUCTED
-                               | MBEDTLS_ASN1_SEQUENCE);
+    ret = pkcs7_get_one_cert(p, end_set, certs);
     if (ret != 0) {
-        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_PKCS7_INVALID_CERT, ret);
+        return ret;
     }
 
-    end_cert = *p + len2;
+    num_of_certs++;
 
-    /*
-     * This is to verify that there is only one signer certificate. It seems it is
-     * not easy to differentiate between the chain vs different signer's certificate.
-     * So, we support only the root certificate and the single signer.
-     * The behaviour would be improved with addition of multiple signer support.
-     */
-    if (end_cert != end_set) {
-        return MBEDTLS_ERR_PKCS7_FEATURE_UNAVAILABLE;
-    }
-
-    if ((ret = mbedtls_x509_crt_parse_der(certs, start, len1)) < 0) {
-        return MBEDTLS_ERR_PKCS7_INVALID_CERT;
+    while (*p != end_set) {
+        ret = pkcs7_get_one_cert(p, end_set, certs);
+        if (ret != 0) {
+            return ret;
+        }
+        num_of_certs++;
     }
 
-    *p = end_cert;
+    *p = end_set;
 
-    /*
-     * Since in this version we strictly support single certificate, and reaching
-     * here implies we have parsed successfully, we return 1.
-     */
-    return 1;
+    return num_of_certs;
 }
 
 /**
-- 
2.25.1