Improve file descriptor closing loops (#14213)

* Add for_each_open_fd() and fix second instance of _SC_OPEN_MAX

* Add argument to allow exclusion of file descriptors from closing

* Fix clang error

* Address review comments

* Use close_range() if possible and replace macros with enums

3 files changed, 82 insertions, 8 deletions

diff --git a/libnetdata/libnetdata.c b/libnetdata/libnetdata.c
index aa7a6d7364..7d86395671 100644
--- a/libnetdata/libnetdata.c
+++ b/libnetdata/libnetdata.c
@@ -1948,3 +1948,70 @@ bool run_command_and_copy_output_to_stdout(const char *command, int max_line_len
     netdata_pclose(NULL, fp, pid);
     return true;
 }
+
+void for_each_open_fd(OPEN_FD_ACTION action, OPEN_FD_EXCLUDE excluded_fds){
+    int fd;
+
+    switch(action){
+        case OPEN_FD_ACTION_CLOSE:
+            if(!(excluded_fds & OPEN_FD_EXCLUDE_STDIN))  (void)close(STDIN_FILENO);
+            if(!(excluded_fds & OPEN_FD_EXCLUDE_STDOUT)) (void)close(STDOUT_FILENO);
+            if(!(excluded_fds & OPEN_FD_EXCLUDE_STDERR)) (void)close(STDERR_FILENO);
+            break;
+        case OPEN_FD_ACTION_FD_CLOEXEC:
+            if(!(excluded_fds & OPEN_FD_EXCLUDE_STDIN))  (void)fcntl(STDIN_FILENO, F_SETFD, FD_CLOEXEC);
+            if(!(excluded_fds & OPEN_FD_EXCLUDE_STDOUT)) (void)fcntl(STDOUT_FILENO, F_SETFD, FD_CLOEXEC);
+            if(!(excluded_fds & OPEN_FD_EXCLUDE_STDERR)) (void)fcntl(STDERR_FILENO, F_SETFD, FD_CLOEXEC);
+            break;
+        default:
+            break; // do nothing
+    }
+
+#if defined(HAVE_CLOSE_RANGE)
+    if(close_range(STDERR_FILENO + 1, ~0U, (action == OPEN_FD_ACTION_FD_CLOEXEC ? CLOSE_RANGE_CLOEXEC : 0)) == 0) return;
+    error("close_range() failed, will try to close fds manually");
+#endif
+
+    DIR *dir = opendir("/proc/self/fd");
+    if (dir == NULL) {
+        struct rlimit rl;
+        int open_max = -1;
+
+        if(getrlimit(RLIMIT_NOFILE, &rl) == 0 && rl.rlim_max != RLIM_INFINITY) open_max = rl.rlim_max;
+#ifdef _SC_OPEN_MAX
+        else open_max = sysconf(_SC_OPEN_MAX);
+#endif
+
+        if (open_max == -1) open_max = 65535; // 65535 arbitrary default if everything else fails
+
+        for (fd = STDERR_FILENO + 1; fd < open_max; fd++) {
+            switch(action){
+                case OPEN_FD_ACTION_CLOSE:
+                    if(fd_is_valid(fd)) (void)close(fd);
+                    break;
+                case OPEN_FD_ACTION_FD_CLOEXEC:
+                    (void)fcntl(fd, F_SETFD, FD_CLOEXEC);
+                    break;
+                default:
+                    break; // do nothing
+            }
+        }
+    } else {
+        struct dirent *entry;
+        while ((entry = readdir(dir)) != NULL) {
+            fd = str2i(entry->d_name);
+            if(unlikely((fd == STDIN_FILENO ) || (fd == STDOUT_FILENO) || (fd == STDERR_FILENO) )) continue;
+            switch(action){
+                case OPEN_FD_ACTION_CLOSE:
+                    if(fd_is_valid(fd)) (void)close(fd);
+                    break;
+                case OPEN_FD_ACTION_FD_CLOEXEC:
+                    (void)fcntl(fd, F_SETFD, FD_CLOEXEC);
+                    break;
+                default:
+                    break; // do nothing
+            }
+        }
+        closedir(dir);
+    }
+}
diff --git a/libnetdata/libnetdata.h b/libnetdata/libnetdata.h
index 7a7fe032ff..56d984dec5 100644
--- a/libnetdata/libnetdata.h
+++ b/libnetdata/libnetdata.h
@@ -432,6 +432,17 @@ static inline char *get_word(char **words, size_t num_words, size_t index) {
 
 bool run_command_and_copy_output_to_stdout(const char *command, int max_line_length);
 
+typedef enum {
+    OPEN_FD_ACTION_CLOSE,
+    OPEN_FD_ACTION_FD_CLOEXEC
+} OPEN_FD_ACTION;
+typedef enum {
+    OPEN_FD_EXCLUDE_STDIN   = 0x01,
+    OPEN_FD_EXCLUDE_STDOUT  = 0x02,
+    OPEN_FD_EXCLUDE_STDERR  = 0x04
+} OPEN_FD_EXCLUDE;
+void for_each_open_fd(OPEN_FD_ACTION action, OPEN_FD_EXCLUDE excluded_fds);
+
 void netdata_cleanup_and_exit(int ret) NORETURN;
 void send_statistics(const char *action, const char *action_result, const char *action_data);
 extern char *netdata_configured_host_prefix;
diff --git a/libnetdata/popen/popen.c b/libnetdata/popen/popen.c
index 57f957f636..e7fc772263 100644
--- a/libnetdata/popen/popen.c
+++ b/libnetdata/popen/popen.c
@@ -163,8 +163,7 @@ static int popene_internal(volatile pid_t *pidptr, char **env, uint8_t flags, FI
     posix_spawnattr_t attr;
     posix_spawn_file_actions_t fa;
 
-    int stdin_fd_to_exclude_from_closing = -1;
-    int stdout_fd_to_exclude_from_closing = -1;
+    unsigned int fds_to_exclude_from_closing = OPEN_FD_EXCLUDE_STDERR;
 
     if(posix_spawn_file_actions_init(&fa)) {
         error("POPEN: posix_spawn_file_actions_init() failed.");
@@ -195,7 +194,7 @@ static int popene_internal(volatile pid_t *pidptr, char **env, uint8_t flags, FI
         if (posix_spawn_file_actions_addopen(&fa, STDIN_FILENO, "/dev/null", O_RDONLY, 0)) {
             error("POPEN: posix_spawn_file_actions_addopen() on stdin to /dev/null failed.");
             // this is not a fatal error
-            stdin_fd_to_exclude_from_closing = STDIN_FILENO;
+            fds_to_exclude_from_closing |= OPEN_FD_EXCLUDE_STDIN;
         }
     }
 
@@ -222,16 +221,13 @@ static int popene_internal(volatile pid_t *pidptr, char **env, uint8_t flags, FI
         if (posix_spawn_file_actions_addopen(&fa, STDOUT_FILENO, "/dev/null", O_WRONLY, 0)) {
             error("POPEN: posix_spawn_file_actions_addopen() on stdout to /dev/null failed.");
             // this is not a fatal error
-            stdout_fd_to_exclude_from_closing = STDOUT_FILENO;
+            fds_to_exclude_from_closing |= OPEN_FD_EXCLUDE_STDOUT;
         }
     }
 
     if(flags & POPEN_FLAG_CLOSE_FD) {
         // Mark all files to be closed by the exec() stage of posix_spawn()
-        for(int i = (int)(sysconf(_SC_OPEN_MAX) - 1); i >= 0; i--) {
-            if(likely(i != STDERR_FILENO && i != stdin_fd_to_exclude_from_closing && i != stdout_fd_to_exclude_from_closing))
-                (void)fcntl(i, F_SETFD, FD_CLOEXEC);
-        }
+        for_each_open_fd(OPEN_FD_ACTION_FD_CLOEXEC, fds_to_exclude_from_closing);
     }
 
     attr_rc = posix_spawnattr_init(&attr);