From 35a4283615ab07ab122feabd0444c86f0ab495ca Mon Sep 17 00:00:00 2001
From: Simon Tatham <anakin@pobox.com>
Date: Mon, 15 Oct 2018 18:53:25 +0100
Subject: [PATCH] Loosen the validity check in get_mp_ssh1.

The SSH-1 spec says that it's legitimate to write an mp-int in which
the prefixed uint16 bit count is greater than the minimum number of
bits required to represent the number. I was enforcing that they had
to be actually equal, on pain of a BinarySource decoding error.
---
 sshbn.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/sshbn.c b/sshbn.c
index 9c36f531..17293762 100644
--- a/sshbn.c
+++ b/sshbn.c
@@ -1588,7 +1588,9 @@ Bignum BinarySource_get_mp_ssh1(BinarySource *src)
         return bignum_from_long(0);
     } else {
         Bignum toret = bignum_from_bytes(bytes.ptr, bytes.len);
-        if (bignum_bitcount(toret) != bitc) {
+        /* SSH-1.5 spec says that it's OK for the prefix uint16 to be
+         * _greater_ than the actual number of bits */
+        if (bignum_bitcount(toret) > bitc) {
             src->err = BSE_INVALID;
             freebn(toret);
             toret = bignum_from_long(0);