[tor-commits] [tor/maint-0.4.3] Extract key length check into a new function, and check more fields.

[nickm at torproject.org]

commit 8abdb394893a1704f885278f5f5d7913cdf516c9
Author: Nick Mathewson <nickm at torproject.org>
Date:   Tue Mar 17 10:04:38 2020 -0400

    Extract key length check into a new function, and check more fields.
    
    In the openssl that I have, it should be safe to only check the size
    of n.  But if I'm wrong, or if other openssls work differently, we
    should check whether any of the fields are too large.
    
    Issue spotted by Teor.
---
 src/lib/crypt_ops/crypto_rsa_openssl.c | 57 +++++++++++++++++++++++++++++++---
 1 file changed, 52 insertions(+), 5 deletions(-)

diff --git a/src/lib/crypt_ops/crypto_rsa_openssl.c b/src/lib/crypt_ops/crypto_rsa_openssl.c
index 0db25f347..6f3ac6fde 100644
--- a/src/lib/crypt_ops/crypto_rsa_openssl.c
+++ b/src/lib/crypt_ops/crypto_rsa_openssl.c
@@ -33,6 +33,7 @@ ENABLE_GCC_WARNING(redundant-decls)
 #include "lib/encoding/binascii.h"
 
 #include <string.h>
+#include <stdbool.h>
 
 /** Declaration for crypto_pk_t structure. */
 struct crypto_pk_t
@@ -564,6 +565,56 @@ crypto_pk_asn1_encode_private(const crypto_pk_t *pk, char *dest,
   return len;
 }
 
+/** Check whether any component of a private key is too large in a way that
+ * seems likely to make verification too expensive. Return true if it's too
+ * long, and false otherwise. */
+static bool
+rsa_private_key_too_long(RSA *rsa, int max_bits)
+{
+  const BIGNUM *n, *e, *p, *q, *d, *dmp1, *dmq1, *iqmp;
+#ifdef OPENSSL_1_1_API
+  n = RSA_get0_n(rsa);
+  e = RSA_get0_e(rsa);
+  p = RSA_get0_p(rsa);
+  q = RSA_get0_q(rsa);
+  d = RSA_get0_d(rsa);
+  dmp1 = RSA_get0_dmp1(rsa);
+  dmq1 = RSA_get0_dmq1(rsa);
+  iqmp = RSA_get0_iqmp(rsa);
+
+  if (RSA_bits(rsa) > max_bits)
+    return true;
+#else
+  n = rsa->n;
+  e = rsa->e;
+  p = rsa->p;
+  q = rsa->q;
+  d = rsa->d;
+  dmp1 = rsa->dmp1;
+  dmq1 = rsa->dmq1;
+  iqmp = rsa->iqmp;
+#endif
+
+  if (n && BN_num_bits(n) > max_bits)
+    return true;
+  if (e && BN_num_bits(e) > max_bits)
+    return true;
+  if (p && BN_num_bits(p) > max_bits)
+    return true;
+  if (q && BN_num_bits(q) > max_bits)
+    return true;
+  if (d && BN_num_bits(d) > max_bits)
+    return true;
+  if (dmp1 && BN_num_bits(dmp1) > max_bits)
+    return true;
+  if (dmq1 && BN_num_bits(dmq1) > max_bits)
+    return true;
+  if (iqmp && BN_num_bits(iqmp) > max_bits)
+    return true;
+
+  return false;
+}
+
 /** Decode an ASN.1-encoded private key from <b>str</b>; return the result on
  * success and NULL on failure.
  *
@@ -584,11 +635,7 @@ crypto_pk_asn1_decode_private(const char *str, size_t len, int max_bits)
     crypto_openssl_log_errors(LOG_WARN,"decoding private key");
     return NULL;
   }
-#ifdef OPENSSL_1_1_API
-  if (max_bits >= 0 && RSA_bits(rsa) > max_bits) {
-#else
-  if (max_bits >= 0 && rsa->n && BN_num_bits(rsa->n) > max_bits) {
-#endif
+  if (max_bits >= 0 && rsa_private_key_too_long(rsa, max_bits)) {
     log_info(LD_CRYPTO, "Private key longer than expected.");
     RSA_free(rsa);
     return NULL;