Dpkg::Exit: Unregister all signal handlers once we have executed them

We should cleanup the handlers to the previous state otherwise we
end up changing the behavior globally, when this should be a local
cleanup behavior.

Closes: #932841

2 files changed, 22 insertions, 3 deletions

diff --git a/debian/changelog b/debian/changelog
index c5bad0b90..3bb18cef3 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -71,6 +71,8 @@ dpkg (1.20.0) UNRELEASED; urgency=medium
     - Dpkg::Checksums: Remove obsolete 'program' property warning.
     - Dpkg::Conf: Remove obsolete methods and obsolete croak for method option.
     - Dpkg::Vendor: Remove obsolete 'keyrings' hook.
+    - Dpkg::Exit: Unregister all signal handlers once we have executed them.
+      Closes: #932841
   * Documentation:
     - man: Fix uncommon wording constructs.
     - man: Use a minus sign for a literal string.
diff --git a/scripts/Dpkg/Exit.pm b/scripts/Dpkg/Exit.pm
index fb51a3abf..53c4981cd 100644
--- a/scripts/Dpkg/Exit.pm
+++ b/scripts/Dpkg/Exit.pm
@@ -52,6 +52,8 @@ Register a code reference into the exit function handlers stack.
 
 sub push_exit_handler {
     my ($func) = shift;
+
+    _setup_exit_handlers() if @handlers == 0;
     push @handlers, $func;
 }
 
@@ -62,6 +64,7 @@ Pop the last registered exit handler from the handlers stack.
 =cut
 
 sub pop_exit_handler {
+    _reset_exit_handlers() if @handlers == 1;
     pop @handlers;
 }
 
@@ -80,9 +83,23 @@ sub _exit_handler {
     exit(127);
 }
 
-$SIG{INT} = \&_exit_handler;
-$SIG{HUP} = \&_exit_handler;
-$SIG{QUIT} = \&_exit_handler;
+my @SIGNAMES = qw(INT HUP QUIT);
+my %SIGOLD;
+
+sub _setup_exit_handlers
+{
+    foreach my $signame (@SIGNAMES) {
+        $SIGOLD{$signame} = $SIG{$signame};
+        $SIG{$signame} = \&_exit_handler;
+    }
+}
+
+sub _reset_exit_handlers
+{
+    foreach my $signame (@SIGNAMES) {
+        $SIG{$signame} = $SIGOLD{$signame};
+    }
+}
 
 =back