1 files changed, 175 insertions, 0 deletions
diff --git a/libpam/pam_modutil_sanitize.c b/libpam/pam_modutil_sanitize.c
new file mode 100644
index 00000000..65f85d01
--- /dev/null
+++ b/libpam/pam_modutil_sanitize.c
@@ -0,0 +1,175 @@
+/*
+ * This file implements the following functions:
+ *   pam_modutil_sanitize_helper_fds:
+ *     redirects standard descriptors, closes all other descriptors.
+ */
+
+#include "pam_modutil_private.h"
+#include <security/pam_ext.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <syslog.h>
+#include <sys/resource.h>
+
+/*
+ * Creates a pipe, closes its write end, redirects fd to its read end.
+ * Returns fd on success, -1 otherwise.
+ */
+static int
+redirect_in_pipe(pam_handle_t *pamh, int fd, const char *name)
+{
+	int in[2];
+
+	if (pipe(in) < 0) {
+		pam_syslog(pamh, LOG_ERR, "Could not create pipe: %m");
+		return -1;
+	}
+
+	close(in[1]);
+
+	if (in[0] == fd)
+		return fd;
+
+	if (dup2(in[0], fd) != fd) {
+		pam_syslog(pamh, LOG_ERR, "dup2 of %s failed: %m", name);
+		fd = -1;
+	}
+
+	close(in[0]);
+	return fd;
+}
+
+/*
+ * Creates a pipe, closes its read end, redirects fd to its write end.
+ * Returns fd on success, -1 otherwise.
+ */
+static int
+redirect_out_pipe(pam_handle_t *pamh, int fd, const char *name)
+{
+	int out[2];
+
+	if (pipe(out) < 0) {
+		pam_syslog(pamh, LOG_ERR, "Could not create pipe: %m");
+		return -1;
+	}
+
+	close(out[0]);
+
+	if (out[1] == fd)
+		return fd;
+
+	if (dup2(out[1], fd) != fd) {
+		pam_syslog(pamh, LOG_ERR, "dup2 of %s failed: %m", name);
+		fd = -1;
+	}
+
+	close(out[1]);
+	return fd;
+}
+
+/*
+ * Opens /dev/null for writing, redirects fd there.
+ * Returns fd on success, -1 otherwise.
+ */
+static int
+redirect_out_null(pam_handle_t *pamh, int fd, const char *name)
+{
+	int null = open("/dev/null", O_WRONLY);
+
+	if (null < 0) {
+		pam_syslog(pamh, LOG_ERR, "open of %s failed: %m", "/dev/null");
+		return -1;
+	}
+
+	if (null == fd)
+		return fd;
+
+	if (dup2(null, fd) != fd) {
+		pam_syslog(pamh, LOG_ERR, "dup2 of %s failed: %m", name);
+		fd = -1;
+	}
+
+	close(null);
+	return fd;
+}
+
+static int
+redirect_out(pam_handle_t *pamh, enum pam_modutil_redirect_fd mode,
+	     int fd, const char *name)
+{
+	switch (mode) {
+		case PAM_MODUTIL_PIPE_FD:
+			if (redirect_out_pipe(pamh, fd, name) < 0)
+				return -1;
+			break;
+		case PAM_MODUTIL_NULL_FD:
+			if (redirect_out_null(pamh, fd, name) < 0)
+				return -1;
+			break;
+		case PAM_MODUTIL_IGNORE_FD:
+			break;
+	}
+	return fd;
+}
+
+/* Closes all descriptors after stderr. */
+static void
+close_fds(void)
+{
+	/*
+	 * An arbitrary upper limit for the maximum file descriptor number
+	 * returned by RLIMIT_NOFILE.
+	 */
+	const int MAX_FD_NO = 65535;
+
+	/* The lower limit is the same as for _POSIX_OPEN_MAX. */
+	const 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;
+
+	for (; fd > STDERR_FILENO; --fd)
+		close(fd);
+}
+
+int
+pam_modutil_sanitize_helper_fds(pam_handle_t *pamh,
+				enum pam_modutil_redirect_fd stdin_mode,
+				enum pam_modutil_redirect_fd stdout_mode,
+				enum pam_modutil_redirect_fd stderr_mode)
+{
+	if (stdin_mode != PAM_MODUTIL_IGNORE_FD &&
+	    redirect_in_pipe(pamh, STDIN_FILENO, "stdin") < 0) {
+		return -1;
+	}
+
+	if (redirect_out(pamh, stdout_mode, STDOUT_FILENO, "stdout") < 0)
+		return -1;
+
+	/*
+	 * If stderr should not be ignored and
+	 * redirect mode for stdout and stderr are the same,
+	 * optimize by redirecting stderr to stdout.
+	 */
+	if (stderr_mode != PAM_MODUTIL_IGNORE_FD &&
+	    stdout_mode == stderr_mode) {
+		if (dup2(STDOUT_FILENO, STDERR_FILENO) != STDERR_FILENO) {
+			pam_syslog(pamh, LOG_ERR,
+				   "dup2 of %s failed: %m", "stderr");
+			return -1;
+		}
+	} else {
+		if (redirect_out(pamh, stderr_mode, STDERR_FILENO, "stderr") < 0)
+			return -1;
+	}
+
+	close_fds();
+	return 0;
+}