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/*
* 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>
#include <dirent.h>
#ifdef HAVE_SYS_VFS_H
#include <sys/vfs.h>
#endif
#ifdef HAVE_LINUX_MAGIC_H
#include <linux/magic.h>
#endif
/*
* 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;
}
/*
* 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_in_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;
}
/* Check if path is in a procfs. */
static int
is_in_procfs(int fd)
{
#if defined HAVE_SYS_VFS_H && defined PROC_SUPER_MAGIC
struct statfs stfs;
if (fstatfs(fd, &stfs) == 0) {
if (stfs.f_type == PROC_SUPER_MAGIC)
return 1;
} else {
return 0;
}
#endif /* HAVE_SYS_VFS_H && PROC_SUPER_MAGIC */
return -1;
}
/* Closes all descriptors after stderr. */
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 unsigned int MAX_FD_NO = 65535;
/* The lower limit is the same as for _POSIX_OPEN_MAX. */
const unsigned int MIN_FD_NO = 20;
/* If /proc is mounted, we can optimize which fd can be closed. */
if ((dir = opendir("/proc/self/fd")) != NULL) {
if ((dfd = dirfd(dir)) >= 0 && is_in_procfs(dfd) > 0) {
while ((dent = readdir(dir)) != NULL) {
fd = atoi(dent->d_name);
if (fd > STDERR_FILENO && fd != dfd)
close(fd);
}
} else {
dfd = -1;
}
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);
}
}
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;
}
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