From 0541a1adf7c25356e7bbd792a8d6ee217a0d92f3 Mon Sep 17 00:00:00 2001
From: Simon Kelley <simon@thekelleys.org.uk>
Date: Mon, 2 Mar 2020 17:10:25 +0000
Subject: [PATCH] Factor out closing all file descriptors for later
 optimisation.

---
 src/dnsmasq.c | 16 +++++++---------
 src/dnsmasq.h |  2 +-
 src/helper.c  |  8 ++------
 src/util.c    |  9 +++++++++
 4 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/src/dnsmasq.c b/src/dnsmasq.c
index 573aac0..10f19ea 100644
--- a/src/dnsmasq.c
+++ b/src/dnsmasq.c
@@ -138,20 +138,18 @@ int main (int argc, char **argv)
     }
 #endif
   
-  /* Close any file descriptors we inherited apart from std{in|out|err} 
-     
-     Ensure that at least stdin, stdout and stderr (fd 0, 1, 2) exist,
+  /* Ensure that at least stdin, stdout and stderr (fd 0, 1, 2) exist,
      otherwise file descriptors we create can end up being 0, 1, or 2 
      and then get accidentally closed later when we make 0, 1, and 2 
      open to /dev/null. Normally we'll be started with 0, 1 and 2 open, 
      but it's not guaranteed. By opening /dev/null three times, we 
      ensure that we're not using those fds for real stuff. */
-  for (i = 0; i < max_fd; i++)
-    if (i != STDOUT_FILENO && i != STDERR_FILENO && i != STDIN_FILENO)
-      close(i);
-    else
-      open("/dev/null", O_RDWR); 
-
+  for (i = 0; i < 3; i++)
+    open("/dev/null", O_RDWR); 
+  
+  /* Close any file descriptors we inherited apart from std{in|out|err} */
+  close_fds(max_fd, -1, -1, -1);
+  
 #ifndef HAVE_LINUX_NETWORK
 #  if !(defined(IP_RECVDSTADDR) && defined(IP_RECVIF) && defined(IP_SENDSRCADDR))
   if (!option_bool(OPT_NOWILD))
diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 6103eb5..c46bfeb 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -1283,7 +1283,7 @@ int memcmp_masked(unsigned char *a, unsigned char *b, int len,
 int expand_buf(struct iovec *iov, size_t size);
 char *print_mac(char *buff, unsigned char *mac, int len);
 int read_write(int fd, unsigned char *packet, int size, int rw);
-
+void close_fds(long max_fd, int spare1, int spare2, int spare3);
 int wildcard_match(const char* wildcard, const char* match);
 int wildcard_matchn(const char* wildcard, const char* match, int num);
 
diff --git a/src/helper.c b/src/helper.c
index 1b260a1..7072cf4 100644
--- a/src/helper.c
+++ b/src/helper.c
@@ -131,12 +131,8 @@ int create_helper(int event_fd, int err_fd, uid_t uid, gid_t gid, long max_fd)
      Don't close err_fd, in case the lua-init fails.
      Note that we have to do this before lua init
      so we don't close any lua fds. */
-  for (max_fd--; max_fd >= 0; max_fd--)
-    if (max_fd != STDOUT_FILENO && max_fd != STDERR_FILENO && 
-	max_fd != STDIN_FILENO && max_fd != pipefd[0] && 
-	max_fd != event_fd && max_fd != err_fd)
-      close(max_fd);
-
+  close_fds(max_fd, pipefd[0], event_fd, err_fd);
+  
 #ifdef HAVE_LUASCRIPT
   if (daemon->luascript)
     {
diff --git a/src/util.c b/src/util.c
index 73bf62a..91b52df 100644
--- a/src/util.c
+++ b/src/util.c
@@ -705,6 +705,15 @@ int read_write(int fd, unsigned char *packet, int size, int rw)
   return 1;
 }
 
+/* close all fds except STDIN, STDOUT and STDERR, spare1, spare2 and spare3 */
+void close_fds(long max_fd, int spare1, int spare2, int spare3) 
+{
+  for (max_fd--; max_fd >= 0; max_fd--)
+    if (max_fd != STDOUT_FILENO && max_fd != STDERR_FILENO && max_fd != STDIN_FILENO &&
+	max_fd != spare1 && max_fd != spare2 && max_fd != spare3)
+      close(max_fd);
+}
+
 /* Basically match a string value against a wildcard pattern.  */
 int wildcard_match(const char* wildcard, const char* match)
 {