openssh unix dev - Apr 2025 - [PATCH] ssh-agent: exit 0 from SIGTERM under systemd socket-activation

When the ssh-agent service is configured to be launched under systemd
socket-activation, the user can inspect the status of the agent with
something like:

    systemctl --user status ssh-agent.service

If the user does:

    systemctl --user stop ssh-agent.service

it causes the `systemd --user` supervisor to send a SIGTERM to the
agent, which terminates while leaving the systemd-managed socket in
place.  That's good, and as expected. (If the user wants to close the
socket, they can do "systemctl --user stop ssh-agent.socket" instead)

But because ssh-agent exits with code 2 in response to a SIGTERM, the
supervisor marks the service as "failed", even though the state of the
supervised service is exactly the same as during session startup (not
running, ready to launch when a client connects to the socket).

This change makes ssh-agent exit cleanly (code 0) in response to a
SIGTERM when launched under socket activation. This aligns the systemd
supervisor's understanding of the state of supervised ssh-agent with
reality.

Signed-off-by: Daniel Kahn Gillmor <dkg at fifthhorseman.net>
---
 ssh-agent.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/ssh-agent.c b/ssh-agent.c
index 55b9f44f4..9617e6ee0 100644
--- a/ssh-agent.c
+++ b/ssh-agent.c
@@ -2238,6 +2238,7 @@ main(int ac, char **av)
 	size_t npfd = 0;
 	u_int maxfds;
 	sigset_t nsigset, osigset;
+	int socket_activated = 0;
 
 	/* Ensure that fds 0, 1 and 2 are open or directed to /dev/null */
 	sanitise_stdfd();
@@ -2389,6 +2390,7 @@ main(int ac, char **av)
 			fatal("bad LISTEN_PID: %d vs pid %d", pid, getpid());
 		debug("using socket activation on fd=3");
 		sock = 3;
+		socket_activated = 1;
 	}
 
 	/* Otherwise, create private directory for agent socket */
@@ -2522,7 +2524,7 @@ skip:
 		sigprocmask(SIG_BLOCK, &nsigset, &osigset);
 		if (signalled_exit != 0) {
 			logit("exiting on signal %d", (int)signalled_exit);
-			cleanup_exit(2);
+			cleanup_exit((signalled_exit == SIGTERM && socket_activated) ? 0 :
2);
 		}
 		if (signalled_keydrop) {
 			logit("signal %d received; removing all keys",
-- 
2.47.2

On Tue 2025-04-15 20:18:34 -0400, Daniel Kahn Gillmor
wrote:
> This change makes ssh-agent exit cleanly (code 0) in response to a
> SIGTERM when launched under socket activation. This aligns the systemd
> supervisor's understanding of the state of supervised ssh-agent with
> reality.
I've also proposed this on github as:
https://github.com/openssh/openssh-portable/pull/565

Thanks for considering this cleanup!

       --dkg
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Just a gentle nudge here: if it's possible to get a review of the
proposed change below, i'd appreciate it!

         --dkg

On Tue 2025-04-15 20:18:34 -0400, Daniel Kahn Gillmor
wrote:
> When the ssh-agent service is configured to be launched under systemd
> socket-activation, the user can inspect the status of the agent with
> something like:
>
>     systemctl --user status ssh-agent.service
>
> If the user does:
>
>     systemctl --user stop ssh-agent.service
>
> it causes the `systemd --user` supervisor to send a SIGTERM to the
> agent, which terminates while leaving the systemd-managed socket in
> place.  That's good, and as expected. (If the user wants to close the
> socket, they can do "systemctl --user stop ssh-agent.socket"
instead)
>
> But because ssh-agent exits with code 2 in response to a SIGTERM, the
> supervisor marks the service as "failed", even though the state
of the
> supervised service is exactly the same as during session startup (not
> running, ready to launch when a client connects to the socket).
>
> This change makes ssh-agent exit cleanly (code 0) in response to a
> SIGTERM when launched under socket activation. This aligns the systemd
> supervisor's understanding of the state of supervised ssh-agent with
> reality.
>
> Signed-off-by: Daniel Kahn Gillmor <dkg at fifthhorseman.net>
> ---
>  ssh-agent.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/ssh-agent.c b/ssh-agent.c
> index 55b9f44f4..9617e6ee0 100644
> --- a/ssh-agent.c
> +++ b/ssh-agent.c
> @@ -2238,6 +2238,7 @@ main(int ac, char **av)
>  	size_t npfd = 0;
>  	u_int maxfds;
>  	sigset_t nsigset, osigset;
> +	int socket_activated = 0;
>  
>  	/* Ensure that fds 0, 1 and 2 are open or directed to /dev/null */
>  	sanitise_stdfd();
> @@ -2389,6 +2390,7 @@ main(int ac, char **av)
>  			fatal("bad LISTEN_PID: %d vs pid %d", pid, getpid());
>  		debug("using socket activation on fd=3");
>  		sock = 3;
> +		socket_activated = 1;
>  	}
>  
>  	/* Otherwise, create private directory for agent socket */
> @@ -2522,7 +2524,7 @@ skip:
>  		sigprocmask(SIG_BLOCK, &nsigset, &osigset);
>  		if (signalled_exit != 0) {
>  			logit("exiting on signal %d", (int)signalled_exit);
> -			cleanup_exit(2);
> +			cleanup_exit((signalled_exit == SIGTERM && socket_activated) ?
0 : 2);
>  		}
>  		if (signalled_keydrop) {
>  			logit("signal %d received; removing all keys",
> -- 
> 2.47.2
>
> _______________________________________________
> openssh-unix-dev mailing list
> openssh-unix-dev at mindrot.org
> https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
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