Fix handling of replies to global requests (#112) The current code assumes that all global requests want / need a reply. This isn't always true and the request itself indicates if it wants a reply or not. It causes a specific problem with [email protected] messages. These are sent by OpenSSH after authentication to inform the client of potential other host keys for the host. This can be used to add a new type of host key or to rotate host keys. The initial information message from the server is sent as a global request, but with want_reply set to false. This means that the server doesn't expect an answer to this message. Instead the client needs to send a prove request as a reply if it wants to receive proof of ownership for the host keys. The bug doesn't cause any current problems with due to how OpenSSH treats receiving the failure message. It instead treats it as a keepalive message and further ignores it. Arguably this is a protocol violation though of Dropbear and it is only accidental that it doesn't cause a problem with OpenSSH. The bug was found when adding host keys support to libssh, which is more strict protocol wise and treats the unexpected failure message an error, also see https://gitlab.com/libssh/libssh-mirror/-/merge_requests/145 for more information. The fix here is to honor the want_reply flag in the global request and to only send a reply if the other side expects a reply.

#include "tommath_private.h"
#ifdef BN_S_MP_RAND_JENKINS_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */

/* Bob Jenkins' http://burtleburtle.net/bob/rand/smallprng.html */
/* Chosen for speed and a good "mix" */
typedef struct {
   uint64_t a;
   uint64_t b;
   uint64_t c;
   uint64_t d;
} ranctx;

static ranctx jenkins_x;

#define rot(x,k) (((x)<<(k))|((x)>>(64-(k))))
static uint64_t s_rand_jenkins_val(void)
{
   uint64_t e = jenkins_x.a - rot(jenkins_x.b, 7);
   jenkins_x.a = jenkins_x.b ^ rot(jenkins_x.c, 13);
   jenkins_x.b = jenkins_x.c + rot(jenkins_x.d, 37);
   jenkins_x.c = jenkins_x.d + e;
   jenkins_x.d = e + jenkins_x.a;
   return jenkins_x.d;
}

void s_mp_rand_jenkins_init(uint64_t seed)
{
   uint64_t i;
   jenkins_x.a = 0xf1ea5eedULL;
   jenkins_x.b = jenkins_x.c = jenkins_x.d = seed;
   for (i = 0uLL; i < 20uLL; ++i) {
      (void)s_rand_jenkins_val();
   }
}

mp_err s_mp_rand_jenkins(void *p, size_t n)
{
   char *q = (char *)p;
   while (n > 0u) {
      int i;
      uint64_t x = s_rand_jenkins_val();
      for (i = 0; (i < 8) && (n > 0u); ++i, --n) {
         *q++ = (char)(x & 0xFFuLL);
         x >>= 8;
      }
   }
   return MP_OKAY;
}

#endif