- naddy@cvs.openbsd.org 2014/06/18 15:42:09

     [sshbuf-getput-crypto.c]
     The ssh_get_bignum functions must accept the same range of bignums
     the corresponding ssh_put_bignum functions create.  This fixes the
     use of 16384-bit RSA keys (bug reported by Eivind Evensen).
     ok djm@

1 files changed, 6 insertions, 4 deletions

diff --git a/sshbuf-getput-crypto.c b/sshbuf-getput-crypto.c
index ca1c7ec65..cfe6f7963 100644
--- a/sshbuf-getput-crypto.c
+++ b/sshbuf-getput-crypto.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: sshbuf-getput-crypto.c,v 1.1 2014/04/30 05:29:56 djm Exp $    */
+/*      $OpenBSD: sshbuf-getput-crypto.c,v 1.2 2014/06/18 15:42:09 naddy Exp $  */
 /*
  * Copyright (c) 2011 Damien Miller
  *
@@ -38,10 +38,12 @@ sshbuf_get_bignum2(struct sshbuf *buf, BIGNUM *v)
 
         if ((r = sshbuf_peek_string_direct(buf, &d, &len)) < 0)
                 return r;
-        /* Refuse negative (MSB set) and overlong bignums */
+        /* Refuse negative (MSB set) bignums */
         if ((len != 0 && (*d & 0x80) != 0))
                 return SSH_ERR_BIGNUM_IS_NEGATIVE;
-        if (len > SSHBUF_MAX_BIGNUM)
+        /* Refuse overlong bignums, allow prepended \0 to avoid MSB set */
+        if (len > SSHBUF_MAX_BIGNUM + 1 ||
+            (len == SSHBUF_MAX_BIGNUM + 1 && *d != 0))
                 return SSH_ERR_BIGNUM_TOO_LARGE;
         if (v != NULL && BN_bin2bn(d, len, v) == NULL)
                 return SSH_ERR_ALLOC_FAIL;
@@ -67,7 +69,7 @@ sshbuf_get_bignum1(struct sshbuf *buf, BIGNUM *v)
                 return SSH_ERR_MESSAGE_INCOMPLETE;
         len_bits = PEEK_U16(d);
         len_bytes = (len_bits + 7) >> 3;
-        if (len_bytes > SSHBUF_MAX_BIGNUM + 1)
+        if (len_bytes > SSHBUF_MAX_BIGNUM)
                 return SSH_ERR_BIGNUM_TOO_LARGE;
         if (sshbuf_len(buf) < 2 + len_bytes)
                 return SSH_ERR_MESSAGE_INCOMPLETE;