diff -up Linux-PAM-1.3.1/libpam/pam_modutil_sanitize.c.fds-closing Linux-PAM-1.3.1/libpam/pam_modutil_sanitize.c

--- Linux-PAM-1.3.1/libpam/pam_modutil_sanitize.c.fds-closing	2017-02-10 11:10:15.000000000 +0100

+++ Linux-PAM-1.3.1/libpam/pam_modutil_sanitize.c	2019-10-16 16:07:31.259021159 +0200

@@ -10,6 +10,7 @@

 #include <fcntl.h>

 #include <syslog.h>

 #include <sys/resource.h>

+#include <dirent.h>

 /*

  * Creates a pipe, closes its write end, redirects fd to its read end.

@@ -116,27 +117,45 @@ redirect_out(pam_handle_t *pamh, enum pa

 static void

 close_fds(void)

 {

+	DIR *dir = NULL;

+	struct dirent *dent;

+	int dfd = -1;

+	int fd;

+	struct rlimit rlim;

+

 	/*

 	 * An arbitrary upper limit for the maximum file descriptor number

 	 * returned by RLIMIT_NOFILE.

 	 */

-	const int MAX_FD_NO = 65535;

+	const unsigned int MAX_FD_NO = 65535;

 	/* The lower limit is the same as for _POSIX_OPEN_MAX. */

-	const int MIN_FD_NO = 20;

+	const unsigned int MIN_FD_NO = 20;

-	int fd;

-	struct rlimit rlim;

-

-	if (getrlimit(RLIMIT_NOFILE, &rlim) || rlim.rlim_max > MAX_FD_NO)

-		fd = MAX_FD_NO;

-	else if (rlim.rlim_max < MIN_FD_NO)

-		fd = MIN_FD_NO;

-	else

-		fd = rlim.rlim_max - 1;

+	/* If /proc is mounted, we can optimize which fd can be closed. */

+	if ((dir = opendir("/proc/self/fd")) != NULL) {

+		if ((dfd = dirfd(dir)) >= 0) {

+			while ((dent = readdir(dir)) != NULL) {

+				fd = atoi(dent->d_name);

+				if (fd > STDERR_FILENO && fd != dfd)

+					close(fd);

+			}

+		}

+		closedir(dir);

+	}

+

+	/* If /proc isn't available, fallback to the previous behavior. */

+	if (dfd < 0) {

+		if (getrlimit(RLIMIT_NOFILE, &rlim) || rlim.rlim_max > MAX_FD_NO)

+			fd = MAX_FD_NO;

+		else if (rlim.rlim_max < MIN_FD_NO)

+			fd = MIN_FD_NO;

+		else

+			fd = rlim.rlim_max - 1;

-	for (; fd > STDERR_FILENO; --fd)

-		close(fd);

+		for (; fd > STDERR_FILENO; --fd)

+			close(fd);

+	}

 }

 int