From 7bc29a9d5cd697290aa056e94ecee6253d3425f8 Mon Sep 17 00:00:00 2001 From: djm Date: Wed, 19 Jul 2023 13:56:33 +0000 Subject: [PATCH] Disallow remote addition of FIDO/PKCS11 provider libraries to ssh-agent by default. The old behaviour of allowing remote clients from loading providers can be restored using `ssh-agent -O allow-remote-pkcs11`. Detection of local/remote clients requires a ssh(1) that supports the `session-bind@openssh.com` extension. Forwarding access to a ssh-agent socket using non-OpenSSH tools may circumvent this control. ok markus@ --- usr.bin/ssh/ssh-agent.1 | 26 ++++++++++++++++++++++---- usr.bin/ssh/ssh-agent.c | 23 +++++++++++++++++++++-- 2 files changed, 43 insertions(+), 6 deletions(-) diff --git a/usr.bin/ssh/ssh-agent.1 b/usr.bin/ssh/ssh-agent.1 index b0bf65da88e..beb81865a63 100644 --- a/usr.bin/ssh/ssh-agent.1 +++ b/usr.bin/ssh/ssh-agent.1 @@ -1,4 +1,4 @@ -.\" $OpenBSD: ssh-agent.1,v 1.75 2022/10/07 06:00:58 jmc Exp $ +.\" $OpenBSD: ssh-agent.1,v 1.76 2023/07/19 13:56:33 djm Exp $ .\" .\" Author: Tatu Ylonen .\" Copyright (c) 1995 Tatu Ylonen , Espoo, Finland @@ -34,7 +34,7 @@ .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" -.Dd $Mdocdate: October 7 2022 $ +.Dd $Mdocdate: July 19 2023 $ .Dt SSH-AGENT 1 .Os .Sh NAME @@ -107,9 +107,27 @@ environment variable). .It Fl O Ar option Specify an option when starting .Nm . -Currently only one option is supported: +Currently two options are supported: +.Cm allow-remote-pkcs11 +and .Cm no-restrict-websafe . -This instructs +.Pp +The +.Cm allow-remote-pkcs11 +option allows clients of a forwarded +.Nm +to load PKCS#11 or FIDO provider libraries. +By default only local clients may perform this operation. +Note that signalling that a +.Nm +client remote is performed by +.Xr ssh 1 , +and use of other tools to forward access to the agent socket may circumvent +this restriction. +.Pp +The +.Cm no-restrict-websafe , +instructs .Nm to permit signatures using FIDO keys that might be web authentication requests. diff --git a/usr.bin/ssh/ssh-agent.c b/usr.bin/ssh/ssh-agent.c index 79b11611326..0b2ee971226 100644 --- a/usr.bin/ssh/ssh-agent.c +++ b/usr.bin/ssh/ssh-agent.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ssh-agent.c,v 1.299 2023/07/10 04:51:26 djm Exp $ */ +/* $OpenBSD: ssh-agent.c,v 1.300 2023/07/19 13:56:33 djm Exp $ */ /* * Author: Tatu Ylonen * Copyright (c) 1995 Tatu Ylonen , Espoo, Finland @@ -156,6 +156,12 @@ char socket_dir[PATH_MAX]; /* Pattern-list of allowed PKCS#11/Security key paths */ static char *allowed_providers; +/* + * Allows PKCS11 providers or SK keys that use non-internal providers to + * be added over a remote connection (identified by session-bind@openssh.com). + */ +static int remote_add_provider; + /* locking */ #define LOCK_SIZE 32 #define LOCK_SALT_SIZE 16 @@ -1215,6 +1221,12 @@ process_add_identity(SocketEntry *e) if (strcasecmp(sk_provider, "internal") == 0) { debug_f("internal provider"); } else { + if (e->nsession_ids != 0 && !remote_add_provider) { + verbose("failed add of SK provider \"%.100s\": " + "remote addition of providers is disabled", + sk_provider); + goto out; + } if (realpath(sk_provider, canonical_provider) == NULL) { verbose("failed provider \"%.100s\": " "realpath: %s", sk_provider, @@ -1378,6 +1390,11 @@ process_add_smartcard_key(SocketEntry *e) error_f("failed to parse constraints"); goto send; } + if (e->nsession_ids != 0 && !remote_add_provider) { + verbose("failed PKCS#11 add of \"%.100s\": remote addition of " + "providers is disabled", provider); + goto send; + } if (realpath(provider, canonical_provider) == NULL) { verbose("failed PKCS#11 add of \"%.100s\": realpath: %s", provider, strerror(errno)); @@ -2032,7 +2049,9 @@ main(int ac, char **av) break; case 'O': if (strcmp(optarg, "no-restrict-websafe") == 0) - restrict_websafe = 0; + restrict_websafe = 0; + else if (strcmp(optarg, "allow-remote-pkcs11") == 0) + remote_add_provider = 1; else fatal("Unknown -O option"); break; -- 2.20.1