place shielded keys (i.e. keys at rest in RAM) into memory allocated

using mmap(3) with MAP_CONCEAL set. This prevents exposure of the
key material in coredumps, etc (this is in addition to other measures
we take in this area).

ok deraadt@

diff --git a/usr.bin/ssh/sshkey.c b/usr.bin/ssh/sshkey.c
index ef9c858..2727aac 100644 (file)
--- a/usr.bin/ssh/sshkey.c
+++ b/usr.bin/ssh/sshkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.c,v 1.143 2024/08/15 00:51:51 djm Exp $ */
+/* $OpenBSD: sshkey.c,v 1.144 2024/08/20 03:48:30 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Alexander von Gernler.  All rights reserved.
@@ -26,6 +26,7 @@
  */
 
 #include <sys/types.h>
+#include <sys/mman.h>
 #include <netinet/in.h>
 
 #ifdef WITH_OPENSSL
@@ -710,6 +711,27 @@ sshkey_sk_cleanup(struct sshkey *k)
        k->sk_key_handle = k->sk_reserved = NULL;
 }
 
+static int
+sshkey_prekey_alloc(u_char **prekeyp, size_t len)
+{
+       u_char *prekey;
+
+       *prekeyp = NULL;
+       if ((prekey = mmap(NULL, SSHKEY_SHIELD_PREKEY_LEN, PROT_READ|PROT_WRITE,
+           MAP_ANON|MAP_PRIVATE|MAP_CONCEAL, -1, 0)) == MAP_FAILED)
+               return SSH_ERR_SYSTEM_ERROR;
+       *prekeyp = prekey;
+       return 0;
+}
+
+static void
+sshkey_prekey_free(void *prekey, size_t len)
+{
+       if (prekey == NULL)
+               return;
+       munmap(prekey, len);
+}
+
 static void
 sshkey_free_contents(struct sshkey *k)
 {
@@ -723,7 +745,7 @@ sshkey_free_contents(struct sshkey *k)
        if (sshkey_is_cert(k))
                cert_free(k->cert);
        freezero(k->shielded_private, k->shielded_len);
-       freezero(k->shield_prekey, k->shield_prekey_len);
+       sshkey_prekey_free(k->shield_prekey, k->shield_prekey_len);
 }
 
 void
@@ -1591,10 +1613,8 @@ sshkey_shield_private(struct sshkey *k)
        }
 
        /* Prepare a random pre-key, and from it an ephemeral key */
-       if ((prekey = malloc(SSHKEY_SHIELD_PREKEY_LEN)) == NULL) {
-               r = SSH_ERR_ALLOC_FAIL;
+       if ((r = sshkey_prekey_alloc(&prekey, SSHKEY_SHIELD_PREKEY_LEN)) != 0)
                goto out;
-       }
        arc4random_buf(prekey, SSHKEY_SHIELD_PREKEY_LEN);
        if ((r = ssh_digest_memory(SSHKEY_SHIELD_PREKEY_HASH,
            prekey, SSHKEY_SHIELD_PREKEY_LEN,
@@ -1672,7 +1692,7 @@ sshkey_shield_private(struct sshkey *k)
        explicit_bzero(keyiv, sizeof(keyiv));
        explicit_bzero(&tmp, sizeof(tmp));
        freezero(enc, enclen);
-       freezero(prekey, SSHKEY_SHIELD_PREKEY_LEN);
+       sshkey_prekey_free(prekey, SSHKEY_SHIELD_PREKEY_LEN);
        sshkey_free(kswap);
        sshbuf_free(prvbuf);
        return r;