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upstream: refactor key constraint parsing in ssh-agent 

Key constraints parsing code previously existed in both the "add regular
key" and "add smartcard key" path. This unifies them but also introduces
more consistency checking: duplicated constraints and constraints that
are nonsensical for a particular situation (e.g. FIDO provider for a
smartcard key) are now banned.

ok markus@

OpenBSD-Commit-ID: 511cb1b1c021ee1d51a4c2d649b937445de7983c
This commit is contained in:
djm@openbsd.org 2021-01-26 00:54:49 +00:00 committed by Damien Miller
parent e0e8bee802
commit 37c70ea8d4
1 changed files with 95 additions and 69 deletions
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164
ssh-agent.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: ssh-agent.c,v 1.270 2021/01/26 00:53:31 djm Exp $ */
/* $OpenBSD: ssh-agent.c,v 1.271 2021/01/26 00:54:49 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@ -574,44 +574,52 @@ reaper(void)
return (deadline - now);
}
static void
process_add_identity(SocketEntry *e)
static int
parse_key_constraints(struct sshbuf *m, struct sshkey *k, time_t *deathp,
u_int *secondsp, int *confirmp, char **sk_providerp)
{
Identity *id;
int success = 0, confirm = 0;
u_int seconds = 0, maxsign;
char *fp, *comment = NULL, *ext_name = NULL, *sk_provider = NULL;
char canonical_provider[PATH_MAX];
time_t death = 0;
struct sshkey *k = NULL;
u_char ctype;
int r = SSH_ERR_INTERNAL_ERROR;
int r;
u_int seconds, maxsign = 0;
char *ext_name = NULL, *sk_provider = NULL;
size_t pos;
struct sshbuf *b = NULL;
debug2_f("entering");
if ((r = sshkey_private_deserialize(e->request, &k)) != 0 ||
k == NULL ||
(r = sshbuf_get_cstring(e->request, &comment, NULL)) != 0) {
error_fr(r, "parse");
goto err;
}
while (sshbuf_len(e->request)) {
if ((r = sshbuf_get_u8(e->request, &ctype)) != 0) {
while (sshbuf_len(m)) {
if ((r = sshbuf_get_u8(m, &ctype)) != 0) {
error_fr(r, "parse constraint type");
goto err;
}
switch (ctype) {
case SSH_AGENT_CONSTRAIN_LIFETIME:
if ((r = sshbuf_get_u32(e->request, &seconds)) != 0) {
if (*deathp != 0) {
error_f("lifetime already set");
goto err;
}
if ((r = sshbuf_get_u32(m, &seconds)) != 0) {
error_fr(r, "parse lifetime constraint");
goto err;
}
death = monotime() + seconds;
*deathp = monotime() + seconds;
*secondsp = seconds;
break;
case SSH_AGENT_CONSTRAIN_CONFIRM:
confirm = 1;
if (*confirmp != 0) {
error_f("confirm already set");
goto err;
}
*confirmp = 1;
break;
case SSH_AGENT_CONSTRAIN_MAXSIGN:
if ((r = sshbuf_get_u32(e->request, &maxsign)) != 0) {
if (k == NULL) {
error_f("maxsign not valid here");
goto err;
}
if (maxsign != 0) {
error_f("maxsign already set");
goto err;
}
if ((r = sshbuf_get_u32(m, &maxsign)) != 0) {
error_fr(r, "parse maxsign constraint");
goto err;
}
@ -621,19 +629,22 @@ process_add_identity(SocketEntry *e)
}
break;
case SSH_AGENT_CONSTRAIN_EXTENSION:
if ((r = sshbuf_get_cstring(e->request,
&ext_name, NULL)) != 0) {
if ((r = sshbuf_get_cstring(m, &ext_name, NULL)) != 0) {
error_fr(r, "parse constraint extension");
goto err;
}
debug_f("constraint ext %s", ext_name);
if (strcmp(ext_name, "sk-provider@openssh.com") == 0) {
if (sk_provider != NULL) {
error("%s already set", ext_name);
if (sk_providerp == NULL) {
error_f("%s not valid here", ext_name);
goto err;
}
if ((r = sshbuf_get_cstring(e->request,
&sk_provider, NULL)) != 0) {
if (*sk_providerp != NULL) {
error_f("%s already set", ext_name);
goto err;
}
if ((r = sshbuf_get_cstring(m,
sk_providerp, NULL)) != 0) {
error_fr(r, "parse %s", ext_name);
goto err;
}
@ -647,20 +658,46 @@ process_add_identity(SocketEntry *e)
default:
error_f("Unknown constraint %d", ctype);
err:
free(sk_provider);
free(ext_name);
sshbuf_reset(e->request);
free(comment);
sshkey_free(k);
goto send;
sshbuf_free(b);
return -1;
}
}
/* success */
return 0;
}
static void
process_add_identity(SocketEntry *e)
{
Identity *id;
int success = 0, confirm = 0;
char *fp, *comment = NULL, *ext_name = NULL, *sk_provider = NULL;
char canonical_provider[PATH_MAX];
time_t death = 0;
u_int seconds = 0;
struct sshkey *k = NULL;
int r = SSH_ERR_INTERNAL_ERROR;
debug2_f("entering");
if ((r = sshkey_private_deserialize(e->request, &k)) != 0 ||
k == NULL ||
(r = sshbuf_get_cstring(e->request, &comment, NULL)) != 0) {
error_fr(r, "parse");
goto out;
}
if (parse_key_constraints(e->request, k, &death, &seconds, &confirm,
&sk_provider) != 0) {
error_f("failed to parse constraints");
sshbuf_reset(e->request);
goto out;
}
if (sk_provider != NULL) {
if (!sshkey_is_sk(k)) {
error("Cannot add provider: %s is not an "
"authenticator-hosted key", sshkey_type(k));
free(sk_provider);
goto send;
goto out;
}
if (strcasecmp(sk_provider, "internal") == 0) {
debug_f("internal provider");
@ -669,8 +706,7 @@ process_add_identity(SocketEntry *e)
verbose("failed provider \"%.100s\": "
"realpath: %s", sk_provider,
strerror(errno));
free(sk_provider);
goto send;
goto out;
}
free(sk_provider);
sk_provider = xstrdup(canonical_provider);
@ -678,17 +714,14 @@ process_add_identity(SocketEntry *e)
allowed_providers, 0) != 1) {
error("Refusing add key: "
"provider %s not allowed", sk_provider);
free(sk_provider);
goto send;
goto out;
}
}
}
if ((r = sshkey_shield_private(k)) != 0) {
error_fr(r, "shield private");
goto err;
goto out;
}
success = 1;
if (lifetime && !death)
death = monotime() + lifetime;
if ((id = lookup_identity(k)) == NULL) {
@ -702,6 +735,7 @@ process_add_identity(SocketEntry *e)
free(id->comment);
free(id->sk_provider);
}
/* success */
id->key = k;
id->comment = comment;
id->death = death;
@ -712,10 +746,18 @@ process_add_identity(SocketEntry *e)
SSH_FP_DEFAULT)) == NULL)
fatal_f("sshkey_fingerprint failed");
debug_f("add %s %s \"%.100s\" (life: %u) (confirm: %u) "
"(provider: %s)", sshkey_ssh_name(k), fp, comment,
seconds, confirm, sk_provider == NULL ? "none" : sk_provider);
"(provider: %s)", sshkey_ssh_name(k), fp, comment, seconds,
confirm, sk_provider == NULL ? "none" : sk_provider);
free(fp);
send:
/* transferred */
k = NULL;
comment = NULL;
sk_provider = NULL;
success = 1;
out:
free(sk_provider);
free(comment);
sshkey_free(k);
send_status(e, success);
}
@ -794,7 +836,7 @@ process_add_smartcard_key(SocketEntry *e)
char *provider = NULL, *pin = NULL, canonical_provider[PATH_MAX];
char **comments = NULL;
int r, i, count = 0, success = 0, confirm = 0;
u_int seconds;
u_int seconds = 0;
time_t death = 0;
u_char type;
struct sshkey **keys = NULL, *k;
@ -806,27 +848,10 @@ process_add_smartcard_key(SocketEntry *e)
error_fr(r, "parse");
goto send;
}
while (sshbuf_len(e->request)) {
if ((r = sshbuf_get_u8(e->request, &type)) != 0) {
error_fr(r, "parse type");
goto send;
}
switch (type) {
case SSH_AGENT_CONSTRAIN_LIFETIME:
if ((r = sshbuf_get_u32(e->request, &seconds)) != 0) {
error_fr(r, "parse lifetime");
goto send;
}
death = monotime() + seconds;
break;
case SSH_AGENT_CONSTRAIN_CONFIRM:
confirm = 1;
break;
default:
error_f("Unknown constraint type %d", type);
goto send;
}
if (parse_key_constraints(e->request, NULL, &death, &seconds, &confirm,
NULL) != 0) {
error_f("failed to parse constraints");
goto send;
}
if (realpath(provider, canonical_provider) == NULL) {
verbose("failed PKCS#11 add of \"%.100s\": realpath: %s",
@ -862,6 +887,7 @@ process_add_smartcard_key(SocketEntry *e)
idtab->nentries++;
success = 1;
}
/* XXX update constraints for existing keys */
sshkey_free(keys[i]);
free(comments[i]);
}