Explicitly unblock signals when selfpiped without signalfd

 This is arguably a bugfix, since selfpipe without signalfd
relies on signals being actually delivered, and a process may
have inherited a nonempty sigprocmask.

 Also use SIG_BLOCK instead of SIG_SETMASK when using
selfpipe_trapset() with signalfd, because we shouldn't unblock
signals that may have previously been blocked. This is also
arguably a bugfix.

 This commit is essential for using the version of s6-linux-init
that blocks SIGINT before disablecad on kernels without signalfd.
Without it, SIGINT never gets unblocked, so it's never delivered
to s6-svscan.

2 files changed, 3 insertions, 3 deletions

diff --git a/src/libstddjb/selfpipe_trap.c b/src/libstddjb/selfpipe_trap.c
index f07db64..090d5ac 100644
--- a/src/libstddjb/selfpipe_trap.c
+++ b/src/libstddjb/selfpipe_trap.c
@@ -38,7 +38,7 @@ int selfpipe_trap (int sig)
 {
   if (selfpipe_fd < 0) return (errno = EBADF, -1) ;
   if (sig_catcha(sig, &selfpipe_ssa) < 0) return -1 ;
-  if (sigaddset(&selfpipe_caught, sig) < 0)
+  if (sigprocmask(SIG_UNBLOCK, sig, 0) < 0 || sigaddset(&selfpipe_caught, sig) < 0)
   {
     int e = errno ;
     sig_restore(sig) ;
diff --git a/src/libstddjb/selfpipe_trapset.c b/src/libstddjb/selfpipe_trapset.c
index ad5ba10..542ad10 100644
--- a/src/libstddjb/selfpipe_trapset.c
+++ b/src/libstddjb/selfpipe_trapset.c
@@ -14,7 +14,7 @@ int selfpipe_trapset (sigset_t const *set)
 {
   sigset_t old ;
   if (selfpipe_fd < 0) return (errno = EBADF, -1) ;
-  if (sigprocmask(SIG_SETMASK, set, &old) < 0) return -1 ;
+  if (sigprocmask(SIG_BLOCK, set, &old) < 0) return -1 ;
   if (signalfd(selfpipe_fd, set, SFD_NONBLOCK | SFD_CLOEXEC) < 0)
   {
     int e = errno ;
@@ -53,7 +53,7 @@ int selfpipe_trapset (sigset_t const *set)
       if (sig_restore(i) < 0) break ;
     }
   }
-  if (i < SKALIBS_NSIG)
+  if (i < SKALIBS_NSIG || sigprocmask(SIG_UNBLOCK, set, 0) < 0)
   {
     int e = errno ;
     sig_restoreto(set, i) ;