sshguard-users

[SSHGuard-users] [PATCH 1/1] sshguard.in: Fix race condition in exit trap

[Gregor H. <gre...@ew...>]

When the sshguard script gets an SIGNAL to exit the clean_and_exit
function is called which calls exit which in turn calls exit 0. This can
in some cases call again clean_and_exit and causes a non-zero exit code.

The sh -x output looks like this in this cases:
...
+ /usr/libexec/sshg-fw-nft-sets
+ clean_and_exit
+ '[' -n  ]
+ exit
+ kill 0
+ clean_and_exit
+ '[' -n  ]
+ exit

~# echo $?
143

Disable the INT/TERM trap in clean_and_exit before exiting to allow a
clean exit.

Signed-off-by: Gregor Herburger <gre...@ew...>
---
 src/sshguard.in | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/sshguard.in b/src/sshguard.in
index bcc5e68ffc04..d4e59f85e1c4 100644
--- a/src/sshguard.in
+++ b/src/sshguard.in
@@ -27,6 +27,7 @@ clean_and_exit() {
     if [ -n "$PID_FILE" ]; then
         rm -f "$PID_FILE"
     fi
+    trap - INT TERM
     exit
 }
 
-- 
2.34.1

Re: [SSHGuard-users] [PATCH 1/1] sshguard.in: Fix race condition in exit trap

[Kevin Z. <kev...@gm...>]

Hi Gregor,

On 5/23/25 4:36 AM, Gregor Herburger wrote:
> When the sshguard script gets an SIGNAL to exit the clean_and_exit
> function is called which calls exit which in turn calls exit 0. This can
> in some cases call again clean_and_exit and causes a non-zero exit code.
Thanks for the investigation and the patch.

The patch seems correct, though would you characterize it as a race 
condition or more of infinite recursion?

Could you also advise what OS/shell you were using when you encountered 
the issue?

Regards,
Kevin

Re: [SSHGuard-users] [PATCH 1/1] sshguard.in: Fix race condition in exit trap

[Gregor H. <gre...@ew...>]

On Tue, May 27, 2025 at 11:42:52AM -0700, Kevin Zheng wrote:

Hi Kevin,
> On 5/23/25 4:36 AM, Gregor Herburger wrote:
> > When the sshguard script gets an SIGNAL to exit the clean_and_exit
> > function is called which calls exit which in turn calls exit 0. This can
> > in some cases call again clean_and_exit and causes a non-zero exit code.
> Thanks for the investigation and the patch.
> 
> The patch seems correct, though would you characterize it as a race
> condition or more of infinite recursion?
> 
Yes I think you are right, it is more of an infinite recursion.
Shall I reword the commit message and resend the patch?

> Could you also advise what OS/shell you were using when you encountered the
> issue?
This happend on a embedded linux system with busybox ash shell. Also
this only happens when the system is under heavy load.

Regards,
Gregor

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Re: [SSHGuard-users] [PATCH 1/1] sshguard.in: Fix race condition in exit trap

[Kevin Z. <kev...@gm...>]

On 5/27/25 10:59 PM, Gregor Herburger wrote:
> Yes I think you are right, it is more of an infinite recursion.
> Shall I reword the commit message and resend the patch?
> 
> This happend on a embedded linux system with busybox ash shell. Also
> this only happens when the system is under heavy load.

Thanks for the information. No need for an extra patch. I'll add a 
comment and include this information in the commit message.

Regards,
Kevin