Hi Danny,
Danny Milosavljevic <dan...@scratchpost.org> skribis:
> what happens when the loop reads the pid file when it contains just half of a
> numeral? It won't detect it, right?
Correct.
I’m proposing the addition below to be on the verrrry safe side.
WDYT?
The weird thing, as I mentioned earlier, is that systemd and Pies do not
protect against truncated PID files, and I couldn’t find any
“documentation” of the problem on the intertubes. For systemd it’s
maybe less of a problem since services are started in a cgroup, I think.
Thanks,
Ludo’.
diff --git a/modules/shepherd/service.scm b/modules/shepherd/service.scm
index b937609..ef27d88 100644
--- a/modules/shepherd/service.scm
+++ b/modules/shepherd/service.scm
@@ -709,10 +709,16 @@ results."
set when starting a service."
(environ))
-(define* (read-pid-file file #:key (max-delay 5))
+(define* (read-pid-file file #:key (max-delay 5)
+ (validate-pid? #f))
"Wait for MAX-DELAY seconds for FILE to show up, and read its content as a
number. Return #f if FILE was not created or does not contain a number;
-otherwise return the number that was read (a PID)."
+otherwise return the number that was read (a PID).
+
+When VALIDATE-PID? is true, succeed if and only if the number that was read is
+the PID of an existing process in the current PID namespace. This test cannot
+be used if FILE might contain a PID from another PID namespace (i.e., the
+daemon writing FILE is running in a separate PID namespace.)"
(define start (current-time))
(let loop ()
@@ -736,11 +742,13 @@ otherwise return the number that was read (a PID)."
(try-again))
((? integer? pid)
;; It's possible, though unlikely, that PID is not a valid PID, for
- ;; instance because writes to FILE did not complete. However, we
- ;; don't do (kill pid 0) because if the process lives in a separate
- ;; PID namespace, then PID is probably invalid in our own
- ;; namespace.
- pid)))
+ ;; instance because writes to FILE did not complete. When
+ ;; VALIDATE-PID? is true, check that PID is valid in the current
+ ;; PID namespace.
+ (if (or (not validate-pid?)
+ (catch-system-error (kill pid 0) #t))
+ pid
+ (try-again)))))
(lambda args
(let ((errno (system-error-errno args)))
(if (= ENOENT errno)
@@ -931,7 +939,8 @@ start."
environment-variables)))
(if pid-file
(match (read-pid-file pid-file
- #:max-delay pid-file-timeout)
+ #:max-delay pid-file-timeout
+ #:validate-pid? #t)
(#f
(catch-system-error (kill pid SIGTERM))
#f)
