Merge pull request #8378 from mschulz-at-hilscher/fixes/issue-8377

Fixes "CSR parsing with critical fields fails"

ChangeLog.d/fix-csr-parsing-with-critical-fields-fails.txt

@@ -0,0 +1,6 @@
+Features
+   * Add new mbedtls_x509_csr_parse_der_with_ext_cb() routine which allows
+     parsing unsupported certificate extensions via user provided callback.
+
+Bugfix
+   * Fix parsing of CSRs with critical extensions.

include/mbedtls/x509_csr.h

@@ -75,7 +75,9 @@ mbedtls_x509write_csr;
 /**
  * \brief          Load a Certificate Signing Request (CSR) in DER format
  *
- * \note           CSR attributes (if any) are currently silently ignored.
+ * \note           Any unsupported requested extensions are silently
+ *                 ignored, unless the critical flag is set, in which case
+ *                 the CSR is rejected.
  *
  * \note           If #MBEDTLS_USE_PSA_CRYPTO is enabled, the PSA crypto
  *                 subsystem must have been initialized by calling
@@ -90,6 +92,67 @@ mbedtls_x509write_csr;
 int mbedtls_x509_csr_parse_der(mbedtls_x509_csr *csr,
                                const unsigned char *buf, size_t buflen);
 
+/**
+ * \brief          The type of certificate extension callbacks.
+ *
+ *                 Callbacks of this type are passed to and used by the
+ *                 mbedtls_x509_csr_parse_der_with_ext_cb() routine when
+ *                 it encounters either an unsupported extension.
+ *                 Future versions of the library may invoke the callback
+ *                 in other cases, if and when the need arises.
+ *
+ * \param p_ctx    An opaque context passed to the callback.
+ * \param csr      The CSR being parsed.
+ * \param oid      The OID of the extension.
+ * \param critical Whether the extension is critical.
+ * \param p        Pointer to the start of the extension value
+ *                 (the content of the OCTET STRING).
+ * \param end      End of extension value.
+ *
+ * \note           The callback must fail and return a negative error code
+ *                 if it can not parse or does not support the extension.
+ *                 When the callback fails to parse a critical extension
+ *                 mbedtls_x509_csr_parse_der_with_ext_cb() also fails.
+ *                 When the callback fails to parse a non critical extension
+ *                 mbedtls_x509_csr_parse_der_with_ext_cb() simply skips
+ *                 the extension and continues parsing.
+ *
+ * \return         \c 0 on success.
+ * \return         A negative error code on failure.
+ */
+typedef int (*mbedtls_x509_csr_ext_cb_t)(void *p_ctx,
+                                         mbedtls_x509_csr const *csr,
+                                         mbedtls_x509_buf const *oid,
+                                         int critical,
+                                         const unsigned char *p,
+                                         const unsigned char *end);
+
+/**
+ * \brief          Load a Certificate Signing Request (CSR) in DER format
+ *
+ * \note           Any unsupported requested extensions are silently
+ *                 ignored, unless the critical flag is set, in which case
+ *                 the result of the callback function decides whether
+ *                 CSR is rejected.
+ *
+ * \note           If #MBEDTLS_USE_PSA_CRYPTO is enabled, the PSA crypto
+ *                 subsystem must have been initialized by calling
+ *                 psa_crypto_init() before calling this function.
+ *
+ * \param csr      CSR context to fill
+ * \param buf      buffer holding the CRL data
+ * \param buflen   size of the buffer
+ * \param cb       A callback invoked for every unsupported certificate
+ *                 extension.
+ * \param p_ctx    An opaque context passed to the callback.
+ *
+ * \return         0 if successful, or a specific X509 error code
+ */
+int mbedtls_x509_csr_parse_der_with_ext_cb(mbedtls_x509_csr *csr,
+                                           const unsigned char *buf, size_t buflen,
+                                           mbedtls_x509_csr_ext_cb_t cb,
+                                           void *p_ctx);
+
 /**
  * \brief          Load a Certificate Signing Request (CSR), DER or PEM format
  *

library/x509_csr.c

@@ -61,13 +61,17 @@ static int x509_csr_get_version(unsigned char **p,
  * Parse CSR extension requests in DER format
  */
 static int x509_csr_parse_extensions(mbedtls_x509_csr *csr,
-                                     unsigned char **p, const unsigned char *end)
+                                     unsigned char **p, const unsigned char *end,
+                                     mbedtls_x509_csr_ext_cb_t cb,
+                                     void *p_ctx)
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t len;
-    unsigned char *end_ext_data;
+    unsigned char *end_ext_data, *end_ext_octet;
+
     while (*p < end) {
         mbedtls_x509_buf extn_oid = { 0, 0, NULL };
+        int is_critical = 0; /* DEFAULT FALSE */
         int ext_type = 0;
 
         /* Read sequence tag */
@@ -88,13 +92,21 @@ static int x509_csr_parse_extensions(mbedtls_x509_csr *csr,
         extn_oid.p = *p;
         *p += extn_oid.len;
 
+        /* Get optional critical */
+        if ((ret = mbedtls_asn1_get_bool(p, end_ext_data, &is_critical)) != 0 &&
+            (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG)) {
+            return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
+        }
+
         /* Data should be octet string type */
         if ((ret = mbedtls_asn1_get_tag(p, end_ext_data, &len,
                                         MBEDTLS_ASN1_OCTET_STRING)) != 0) {
             return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
         }
 
-        if (*p + len != end_ext_data) {
+        end_ext_octet = *p + len;
+
+        if (end_ext_octet != end_ext_data) {
             return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
                                      MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
         }
@@ -104,7 +116,28 @@ static int x509_csr_parse_extensions(mbedtls_x509_csr *csr,
          */
         ret = mbedtls_oid_get_x509_ext_type(&extn_oid, &ext_type);
 
-        if (ret == 0) {
+        if (ret != 0) {
+            /* Give the callback (if any) a chance to handle the extension */
+            if (cb != NULL) {
+                ret = cb(p_ctx, csr, &extn_oid, is_critical, *p, end_ext_octet);
+                if (ret != 0 && is_critical) {
+                    return ret;
+                }
+                *p = end_ext_octet;
+                continue;
+            }
+
+            /* No parser found, skip extension */
+            *p = end_ext_octet;
+
+            if (is_critical) {
+                /* Data is marked as critical: fail */
+                return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
+                                         MBEDTLS_ERR_ASN1_UNEXPECTED_TAG);
+            }
+            continue;
+        }
+
         /* Forbid repeated extensions */
         if ((csr->ext_types & ext_type) != 0) {
             return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
@@ -138,10 +171,17 @@ static int x509_csr_parse_extensions(mbedtls_x509_csr *csr,
                 }
                 break;
             default:
-                    break;
+                /*
+                 * If this is a non-critical extension, which the oid layer
+                 * supports, but there isn't an x509 parser for it,
+                 * skip the extension.
+                 */
+                if (is_critical) {
+                    return MBEDTLS_ERR_X509_FEATURE_UNAVAILABLE;
+                } else {
+                    *p = end_ext_octet;
                 }
         }
-        *p = end_ext_data;
     }
 
     if (*p != end) {
@@ -156,7 +196,9 @@ static int x509_csr_parse_extensions(mbedtls_x509_csr *csr,
  * Parse CSR attributes in DER format
  */
 static int x509_csr_parse_attributes(mbedtls_x509_csr *csr,
-                                     const unsigned char *start, const unsigned char *end)
+                                     const unsigned char *start, const unsigned char *end,
+                                     mbedtls_x509_csr_ext_cb_t cb,
+                                     void *p_ctx)
 {
     int ret;
     size_t len;
@@ -195,7 +237,7 @@ static int x509_csr_parse_attributes(mbedtls_x509_csr *csr,
                 return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
             }
 
-            if ((ret = x509_csr_parse_extensions(csr, p, *p + len)) != 0) {
+            if ((ret = x509_csr_parse_extensions(csr, p, *p + len, cb, p_ctx)) != 0) {
                 return ret;
             }
 
@@ -219,8 +261,10 @@ static int x509_csr_parse_attributes(mbedtls_x509_csr *csr,
 /*
  * Parse a CSR in DER format
  */
-int mbedtls_x509_csr_parse_der(mbedtls_x509_csr *csr,
+static int mbedtls_x509_csr_parse_der_internal(mbedtls_x509_csr *csr,
-                               const unsigned char *buf, size_t buflen)
+                                               const unsigned char *buf, size_t buflen,
+                                               mbedtls_x509_csr_ext_cb_t cb,
+                                               void *p_ctx)
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t len;
@@ -344,7 +388,7 @@ int mbedtls_x509_csr_parse_der(mbedtls_x509_csr *csr,
         return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_FORMAT, ret);
     }
 
-    if ((ret = x509_csr_parse_attributes(csr, p, p + len)) != 0) {
+    if ((ret = x509_csr_parse_attributes(csr, p, p + len, cb, p_ctx)) != 0) {
         mbedtls_x509_csr_free(csr);
         return ret;
     }
@@ -383,6 +427,26 @@ int mbedtls_x509_csr_parse_der(mbedtls_x509_csr *csr,
     return 0;
 }
 
+/*
+ * Parse a CSR in DER format
+ */
+int mbedtls_x509_csr_parse_der(mbedtls_x509_csr *csr,
+                               const unsigned char *buf, size_t buflen)
+{
+    return mbedtls_x509_csr_parse_der_internal(csr, buf, buflen, NULL, NULL);
+}
+
+/*
+ * Parse a CSR in DER format with callback for unknown extensions
+ */
+int mbedtls_x509_csr_parse_der_with_ext_cb(mbedtls_x509_csr *csr,
+                                           const unsigned char *buf, size_t buflen,
+                                           mbedtls_x509_csr_ext_cb_t cb,
+                                           void *p_ctx)
+{
+    return mbedtls_x509_csr_parse_der_internal(csr, buf, buflen, cb, p_ctx);
+}
+
 /*
  * Parse a CSR, allowing for PEM or raw DER encoding
  */

tests/suites/test_suite_x509parse.data

@@ -2940,6 +2940,26 @@ X509 CSR ASN.1 (OK)
 depends_on:MBEDTLS_PK_CAN_ECDSA_SOME:MBEDTLS_ECP_HAVE_SECP256R1:MBEDTLS_MD_CAN_SHA1:!MBEDTLS_X509_REMOVE_INFO
 mbedtls_x509_csr_parse:"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":"CSR version   \: 1\nsubject name  \: C=NL, O=PolarSSL, CN=localhost\nsigned using  \: ECDSA with SHA1\nEC key size   \: 256 bits\n\nkey usage         \: Digital Signature, Non Repudiation, Key Encipherment\n":0
 
+X509 CSR ASN.1 (Unsupported critical extension, critical=true)
+depends_on:MBEDTLS_PK_CAN_ECDSA_SOME:MBEDTLS_ECP_HAVE_SECP256R1:MBEDTLS_MD_CAN_SHA256:!MBEDTLS_X509_REMOVE_INFO
+mbedtls_x509_csr_parse:"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":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS+MBEDTLS_ERR_ASN1_UNEXPECTED_TAG
+
+X509 CSR ASN.1 (Unsupported non-critical extension, critical=false)
+depends_on:MBEDTLS_PK_CAN_ECDSA_SOME:MBEDTLS_ECP_HAVE_SECP256R1:MBEDTLS_MD_CAN_SHA256:!MBEDTLS_X509_REMOVE_INFO
+mbedtls_x509_csr_parse:"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":"CSR version   \: 1\nsubject name  \: CN=Self signed test, C=DE, O=AuthCrtDB Test\nsigned using  \: ECDSA with SHA256\nEC key size   \: 256 bits\n":0
+
+X509 CSR ASN.1 (Unsupported non-critical extension, critical undefined)
+depends_on:MBEDTLS_PK_CAN_ECDSA_SOME:MBEDTLS_ECP_HAVE_SECP256R1:MBEDTLS_MD_CAN_SHA256:!MBEDTLS_X509_REMOVE_INFO
+mbedtls_x509_csr_parse:"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":"CSR version   \: 1\nsubject name  \: CN=Self signed test, C=DE, O=AuthCrtDB Test\nsigned using  \: ECDSA with SHA256\nEC key size   \: 256 bits\n":0
+
+X509 CSR ASN.1 (Unsupported critical extension accepted by callback, critical=true)
+depends_on:MBEDTLS_PK_CAN_ECDSA_SOME:MBEDTLS_ECP_HAVE_SECP256R1:MBEDTLS_MD_CAN_SHA256:!MBEDTLS_X509_REMOVE_INFO
+mbedtls_x509_csr_parse_with_ext_cb:"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":"CSR version   \: 1\nsubject name  \: CN=Self signed test, C=DE, O=AuthCrtDB Test\nsigned using  \: ECDSA with SHA256\nEC key size   \: 256 bits\n":0:1
+
+X509 CSR ASN.1 (Unsupported critical extension rejected by callback, critical=true)
+depends_on:MBEDTLS_PK_CAN_ECDSA_SOME:MBEDTLS_ECP_HAVE_SECP256R1:MBEDTLS_MD_CAN_SHA256:!MBEDTLS_X509_REMOVE_INFO
+mbedtls_x509_csr_parse_with_ext_cb:"308201233081cb02010030413119301706035504030c1053656c66207369676e65642074657374310b300906035504061302444531173015060355040a0c0e41757468437274444220546573743059301306072a8648ce3d020106082a8648ce3d03010703420004c11ebb9951848a436ca2c8a73382f24bbb6c28a92e401d4889b0c361f377b92a8b0497ff2f5a5f6057ae85f704ab1850bef075914f68ed3aeb15a1ff1ebc0dc6a028302606092a864886f70d01090e311930173015060b2b0601040183890c8622020101ff0403010101300a06082a8648ce3d040302034700304402200c4108fd098525993d3fd5b113f0a1ead8750852baf55a2f8e670a22cabc0ba1022034db93a0fcb993912adcf2ea8cb4b66389af30e264d43c0daea03255e45d2ccc":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS+MBEDTLS_ERR_ASN1_UNEXPECTED_TAG:0
+
 X509 CSR ASN.1 (bad first tag)
 mbedtls_x509_csr_parse:"3100":"":MBEDTLS_ERR_X509_INVALID_FORMAT
 

tests/suites/test_suite_x509parse.function

@@ -250,7 +250,8 @@ int verify_parse_san(mbedtls_x509_subject_alternative_name *san,
 
                 ret = mbedtls_oid_get_numeric_string(p,
                                                      n,
-                                                     &san->san.other_name.value.hardware_module_name.oid);
+                                                     &san->san.other_name.value.hardware_module_name
+                                                     .oid);
                 MBEDTLS_X509_SAFE_SNPRINTF;
 
                 ret = mbedtls_snprintf(p, n, ", hardware serial number : ");
@@ -413,6 +414,35 @@ int parse_crt_ext_cb(void *p_ctx, mbedtls_x509_crt const *crt, mbedtls_x509_buf
     }
 }
 #endif /* MBEDTLS_X509_CRT_PARSE_C */
+
+#if defined(MBEDTLS_X509_CSR_PARSE_C)
+int parse_csr_ext_accept_cb(void *p_ctx, mbedtls_x509_csr const *csr, mbedtls_x509_buf const *oid,
+                            int critical, const unsigned char *cp, const unsigned char *end)
+{
+    (void) p_ctx;
+    (void) csr;
+    (void) oid;
+    (void) critical;
+    (void) cp;
+    (void) end;
+
+    return 0;
+}
+
+int parse_csr_ext_reject_cb(void *p_ctx, mbedtls_x509_csr const *csr, mbedtls_x509_buf const *oid,
+                            int critical, const unsigned char *cp, const unsigned char *end)
+{
+    (void) p_ctx;
+    (void) csr;
+    (void) oid;
+    (void) critical;
+    (void) cp;
+    (void) end;
+
+    return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
+                             MBEDTLS_ERR_ASN1_UNEXPECTED_TAG);
+}
+#endif /* MBEDTLS_X509_CSR_PARSE_C */
 /* END_HEADER */
 
 /* BEGIN_CASE depends_on:MBEDTLS_X509_CRT_PARSE_C */
@@ -1247,6 +1277,36 @@ exit:
 }
 /* END_CASE */
 
+/* BEGIN_CASE depends_on:MBEDTLS_X509_CSR_PARSE_C:!MBEDTLS_X509_REMOVE_INFO */
+void mbedtls_x509_csr_parse_with_ext_cb(data_t *csr_der, char *ref_out, int ref_ret, int accept)
+{
+    mbedtls_x509_csr csr;
+    char my_out[1000];
+    int my_ret;
+
+    mbedtls_x509_csr_init(&csr);
+    USE_PSA_INIT();
+
+    memset(my_out, 0, sizeof(my_out));
+
+    my_ret = mbedtls_x509_csr_parse_der_with_ext_cb(&csr, csr_der->x, csr_der->len,
+                                                    accept ? parse_csr_ext_accept_cb :
+                                                    parse_csr_ext_reject_cb,
+                                                    NULL);
+    TEST_EQUAL(my_ret, ref_ret);
+
+    if (ref_ret == 0) {
+        size_t my_out_len = mbedtls_x509_csr_info(my_out, sizeof(my_out), "", &csr);
+        TEST_EQUAL(my_out_len, strlen(ref_out));
+        TEST_EQUAL(strcmp(my_out, ref_out), 0);
+    }
+
+exit:
+    mbedtls_x509_csr_free(&csr);
+    USE_PSA_DONE();
+}
+/* END_CASE */
+
 /* BEGIN_CASE depends_on:MBEDTLS_FS_IO:MBEDTLS_X509_CSR_PARSE_C:!MBEDTLS_X509_REMOVE_INFO */
 void mbedtls_x509_csr_parse_file(char *csr_file, char *ref_out, int ref_ret)
 {