From 7b36e30a8f599942379909f5ec39456e010488b6 Mon Sep 17 00:00:00 2001
From: Laurent Bercot <ska-skaware@skarnet.org>
Date: Sun, 18 Aug 2024 03:35:41 +0000
Subject:  Tentatively fix selfpipe clobbering by notification-fd

Signed-off-by: Laurent Bercot <ska@appnovation.com>
---
 AUTHORS                        |  1 +
 src/supervision/s6-supervise.c | 33 +++++++++++++++++++++++----------
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/AUTHORS b/AUTHORS
index 47030d4..5f685c9 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -42,3 +42,4 @@ Thanks to:
   Oliver Schad <oliver.schad@automatic-server.com>
   Alex Kiernan <alex.kiernan@gmail.com>
   Earl Chew <earl_chew@yahoo.com>
+  Saj Goonatilleke <saj@discourse.org>
diff --git a/src/supervision/s6-supervise.c b/src/supervision/s6-supervise.c
index c0a3edb..86c7709 100644
--- a/src/supervision/s6-supervise.c
+++ b/src/supervision/s6-supervise.c
@@ -142,6 +142,15 @@ static void set_down_and_ready (char const *s, unsigned int n)
   ftrigw_notifyb_nosig(S6_SUPERVISE_EVENTDIR, s, n) ;
 }
 
+static int check_available_fd (int fd, char const *name)
+{
+  int r = fd > maxfd ? (errno = EMFILE, -1) : fcntl(fd, F_GETFD) ;
+  if (r == -1 && errno == EBADF) return 1 ;
+  if (r == -1) strerr_warnwu3sys("check availability of ", name, " (waiting 60 seconds)") ;
+  else strerr_warnw3x(name, " already used internally, please modify its value!", " (waiting 60 seconds)") ;
+  return 0 ;
+}
+
 
 /* The action array. */
 
@@ -298,7 +307,11 @@ static void trystart (void)
 
   if (read_uint("lock-fd", &lk))
   {
-    if (lk > maxfd) strerr_warnw2x("invalid ", "lock-fd") ;
+    if (!check_available_fd(lk, "lock-fd"))
+    {
+      settimeout(60) ;
+      return ;
+    }
     else
     {
       struct stat st ;
@@ -306,14 +319,14 @@ static void trystart (void)
       int lfd = open_write(SLCK) ;
       if (lfd == -1)
       {
-        settimeout(60) ;
         strerr_warnwu4sys("open ", SLCK, " for writing", " (waiting 60 seconds)") ;
-        goto errn ;
+        settimeout(60) ;
+        return ;
       }
       if (fstat(lfd, &st) == -1)
       {
-        settimeout(60) ;
         strerr_warnwu3sys("stat ", SLCK, " (waiting 60 seconds)") ;
+        settimeout(60) ;
         fd_close(lfd) ;
         return ;
       }
@@ -325,13 +338,13 @@ static void trystart (void)
       islocked = fd_islocked(lfd) ;
       if (islocked == -1)
       {
-        settimeout(60) ;
         strerr_warnwu3sys("read lock state on ", SLCK, " (waiting 60 seconds)") ;
+        settimeout(60) ;
         fd_close(lfd) ;
         return ;
       }
       if (islocked)
-        strerr_warnw1x("another instance of the service is already running, child will block") ;
+        strerr_warni1x("another instance of the service is already running, child will block") ;
       fd_close(lfd) ;
       lkfmt[uint_fmt(lkfmt, lk)] = 0 ;
       orig = 0 ;
@@ -340,11 +353,11 @@ static void trystart (void)
 
   if (read_uint("notification-fd", &notif))
   {
-    if (notif > maxfd) strerr_warnw2x("invalid ", "notification-fd") ;
-    if (!orig && notif == lk)
+    if (!check_available_fd(notif, "notification-fd"))
     {
-      settimeout_infinite() ;
-      strerr_warnwu1x("start service: notification-fd and lock-fd are the same") ;
+      settimeout(60) ;
+      if (!orig && notif == lk)
+      strerr_warnw1x("notification-fd and lock-fd are the same") ;
       return ;
     }
     if (pipe(notifyp) == -1)
-- 
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