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upstream: ssh-agent: record failed session-bind attempts 

Record failed attempts to session-bind a connection and refuse signing
operations on that connection henceforth.

Prevents a future situation where we add a new hostkey type that is not
recognised by an older ssh-agent, that consequently causes session-bind
to fail (this situation is only likely to arise when people mix ssh(1)
and ssh-agent(1) of different versions on the same host). Previously,
after such a failure the agent socket would be considered unbound and
not subject to restriction.

Spotted by Jann Horn

OpenBSD-Commit-ID: b0fdd023e920aa4831413f640de4c5307b53552e
This commit is contained in:
djm@openbsd.org 2023-12-18 14:48:08 +00:00 committed by Damien Miller
parent 7ef3787c84
commit 6d51feab15
No known key found for this signature in database
1 changed files with 15 additions and 3 deletions
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18
ssh-agent.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: ssh-agent.c,v 1.302 2023/12/18 14:46:56 djm Exp $ */ /* $OpenBSD: ssh-agent.c,v 1.303 2023/12/18 14:48:08 djm Exp $ */
/* /*
* Author: Tatu Ylonen <ylo@cs.hut.fi> * Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@ -130,6 +130,7 @@ typedef struct socket_entry {
struct sshbuf *request; struct sshbuf *request;
size_t nsession_ids; size_t nsession_ids;
struct hostkey_sid *session_ids; struct hostkey_sid *session_ids;
int session_bind_attempted;
} SocketEntry; } SocketEntry;
u_int sockets_alloc = 0; u_int sockets_alloc = 0;
@ -477,6 +478,10 @@ identity_permitted(Identity *id, SocketEntry *e, char *user,
e->nsession_ids, id->ndest_constraints); e->nsession_ids, id->ndest_constraints);
if (id->ndest_constraints == 0) if (id->ndest_constraints == 0)
return 0; /* unconstrained */ return 0; /* unconstrained */
if (e->session_bind_attempted && e->nsession_ids == 0) {
error_f("previous session bind failed on socket");
return -1;
}
if (e->nsession_ids == 0) if (e->nsession_ids == 0)
return 0; /* local use */ return 0; /* local use */
/* /*
@ -556,6 +561,12 @@ identity_permitted(Identity *id, SocketEntry *e, char *user,
return 0; return 0;
} }
static int
socket_is_remote(SocketEntry *e)
{
return e->session_bind_attempted || (e->nsession_ids != 0);
}
/* return matching private key for given public key */ /* return matching private key for given public key */
static Identity * static Identity *
lookup_identity(struct sshkey *key) lookup_identity(struct sshkey *key)
@ -1367,7 +1378,7 @@ process_add_identity(SocketEntry *e)
if (strcasecmp(sk_provider, "internal") == 0) { if (strcasecmp(sk_provider, "internal") == 0) {
debug_f("internal provider"); debug_f("internal provider");
} else { } else {
if (e->nsession_ids != 0 && !remote_add_provider) { if (socket_is_remote(e) && !remote_add_provider) {
verbose("failed add of SK provider \"%.100s\": " verbose("failed add of SK provider \"%.100s\": "
"remote addition of providers is disabled", "remote addition of providers is disabled",
sk_provider); sk_provider);
@ -1565,7 +1576,7 @@ process_add_smartcard_key(SocketEntry *e)
goto send; goto send;
} }
dump_dest_constraints(__func__, dest_constraints, ndest_constraints); dump_dest_constraints(__func__, dest_constraints, ndest_constraints);
if (e->nsession_ids != 0 && !remote_add_provider) { if (socket_is_remote(e) && !remote_add_provider) {
verbose("failed PKCS#11 add of \"%.100s\": remote addition of " verbose("failed PKCS#11 add of \"%.100s\": remote addition of "
"providers is disabled", provider); "providers is disabled", provider);
goto send; goto send;
@ -1680,6 +1691,7 @@ process_ext_session_bind(SocketEntry *e)
u_char fwd = 0; u_char fwd = 0;
debug2_f("entering"); debug2_f("entering");
e->session_bind_attempted = 1;
if ((r = sshkey_froms(e->request, &key)) != 0 || if ((r = sshkey_froms(e->request, &key)) != 0 ||
(r = sshbuf_froms(e->request, &sid)) != 0 || (r = sshbuf_froms(e->request, &sid)) != 0 ||
(r = sshbuf_froms(e->request, &sig)) != 0 || (r = sshbuf_froms(e->request, &sig)) != 0 ||