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Linux: Require properly configured /dev/pts for PTYs

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Current systems do not have BSD terminals, so the fallback code in
posix_openpt/getpt does not do anything.  Also remove the file system
check for /dev/pts.  Current systems always have a devpts file system
mounted there if /dev/ptmx exists.

grantpt is now essentially a no-op.  It only verifies that the
argument is a ptmx-descriptor.  Therefore, this change indirectly
addresses bug 24941.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
This commit is contained in:
Florian Weimer 2020-10-07 14:55:04 +02:00
parent 0f9793a556
commit 27fe5f2e67
6 changed files with 60 additions and 209 deletions
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11
INSTALL
View File

@ -188,14 +188,9 @@ if 'CFLAGS' is specified it must enable optimization. For example:
'--enable-pt_chown'
The file 'pt_chown' is a helper binary for 'grantpt' (*note
Pseudo-Terminals: Allocation.) that is installed setuid root to fix
up pseudo-terminal ownership. It is not built by default because
systems using the Linux kernel are commonly built with the 'devpts'
filesystem enabled and mounted at '/dev/pts', which manages
pseudo-terminal ownership automatically. By using
'--enable-pt_chown', you may build 'pt_chown' and install it setuid
and owned by 'root'. The use of 'pt_chown' introduces additional
security risks to the system and you should enable it only if you
understand and accept those risks.
up pseudo-terminal ownership on GNU/Hurd. It is not required on
GNU/Linux, and the GNU C Library will not use the installed
'pt_chown' program when configured with '--enable-pt_chown'.
'--disable-werror'
By default, the GNU C Library is built with '-Werror'. If you wish

12
NEWS
View File

@ -35,7 +35,17 @@ Deprecated and removed features, and other changes affecting compatibility:
Changes to build and runtime requirements:
[Add changes to build and runtime requirements here]
* On Linux, the system administrator needs to configure /dev/pts with
the intended access modes for pseudo-terminals. glibc no longer
attemps to adjust permissions of terminal devices. The previous glibc
defaults ("tty" group, user read/write and group write) already
corresponded to what most systems used, so that grantpt did not
perform any adjustments.
* On Linux, the posix_openpt and getpt functions no longer attempt to
use legacy (BSD) pseudo-terminals and assume that if /dev/ptmx exists
(and pseudo-terminals are supported), a devpts file system is mounted
on /dev/pts. Current systems already meet these requirements.
Security related changes:

11
manual/install.texi
View File

@ -218,14 +218,9 @@ increased program load times.
@item --enable-pt_chown
The file @file{pt_chown} is a helper binary for @code{grantpt}
(@pxref{Allocation, Pseudo-Terminals}) that is installed setuid root to
fix up pseudo-terminal ownership. It is not built by default because
systems using the Linux kernel are commonly built with the @code{devpts}
filesystem enabled and mounted at @file{/dev/pts}, which manages
pseudo-terminal ownership automatically. By using
@samp{--enable-pt_chown}, you may build @file{pt_chown} and install it
setuid and owned by @code{root}. The use of @file{pt_chown} introduces
additional security risks to the system and you should enable it only if
you understand and accept those risks.
fix up pseudo-terminal ownership on GNU/Hurd. It is not required on
GNU/Linux, and @theglibc{} will not use the installed @file{pt_chown}
program when configured with @option{--enable-pt_chown}.
@item --disable-werror
By default, @theglibc{} is built with @option{-Werror}. If you wish

67
sysdeps/unix/sysv/linux/getpt.c
View File

@ -16,69 +16,18 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <paths.h>
#include <sys/statfs.h>
#include "linux_fsinfo.h"
/* Path to the master pseudo terminal cloning device. */
#define _PATH_DEVPTMX _PATH_DEV "ptmx"
/* Directory containing the UNIX98 pseudo terminals. */
#define _PATH_DEVPTS _PATH_DEV "pts"
/* Prototype for function that opens BSD-style master pseudo-terminals. */
extern int __bsd_getpt (void) attribute_hidden;
/* Open a master pseudo terminal and return its file descriptor. */
int
__posix_openpt (int oflag)
{
static int have_no_dev_ptmx;
int fd;
if (!have_no_dev_ptmx)
{
fd = __open (_PATH_DEVPTMX, oflag);
if (fd != -1)
{
struct statfs fsbuf;
static int devpts_mounted;
/* Check that the /dev/pts filesystem is mounted
or if /dev is a devfs filesystem (this implies /dev/pts). */
if (devpts_mounted
|| (__statfs (_PATH_DEVPTS, &fsbuf) == 0
&& fsbuf.f_type == DEVPTS_SUPER_MAGIC)
|| (__statfs (_PATH_DEV, &fsbuf) == 0
&& fsbuf.f_type == DEVFS_SUPER_MAGIC))
{
/* Everything is ok. */
devpts_mounted = 1;
return fd;
}
/* If /dev/pts is not mounted then the UNIX98 pseudo terminals
are not usable. */
__close (fd);
have_no_dev_ptmx = 1;
__set_errno (ENOENT);
}
else
{
if (errno == ENOENT || errno == ENODEV)
have_no_dev_ptmx = 1;
else
return -1;
}
}
else
__set_errno (ENOENT);
return -1;
return __open (_PATH_DEVPTMX, oflag);
}
weak_alias (__posix_openpt, posix_openpt)
@ -86,16 +35,6 @@ weak_alias (__posix_openpt, posix_openpt)
int
__getpt (void)
{
int fd = __posix_openpt (O_RDWR);
if (fd == -1)
fd = __bsd_getpt ();
return fd;
return __posix_openpt (O_RDWR);
}
#define PTYNAME1 "pqrstuvwxyzabcde";
#define PTYNAME2 "0123456789abcdef";
#define __getpt __bsd_getpt
#define HAVE_POSIX_OPENPT
#include <sysdeps/unix/bsd/getpt.c>
weak_alias (__getpt, getpt)

73
sysdeps/unix/sysv/linux/grantpt.c
View File

@ -1,44 +1,41 @@
#include <assert.h>
#include <ctype.h>
#include <dirent.h>
/* grantpt implementation for Linux.
Copyright (C) 1998-2020 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Zack Weinberg <zack@rabi.phys.columbia.edu>, 1998.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <fcntl.h>
#include <paths.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <termios.h>
#include <not-cancel.h>
#include "pty-private.h"
#if HAVE_PT_CHOWN
/* Close all file descriptors except the one specified. */
static void
close_all_fds (void)
int
grantpt (int fd)
{
DIR *dir = __opendir ("/proc/self/fd");
if (dir != NULL)
{
struct dirent64 *d;
while ((d = __readdir64 (dir)) != NULL)
if (isdigit (d->d_name[0]))
{
char *endp;
long int fd = strtol (d->d_name, &endp, 10);
if (*endp == '\0' && fd != PTY_FILENO && fd != dirfd (dir))
__close_nocancel_nostatus (fd);
}
/* Without pt_chown on Linux, we have delegated the creation of the
pty node with the right group and permission mode to the kernel, and
non-root users are unlikely to be able to change it. Therefore let's
consider that POSIX enforcement is the responsibility of the whole
system and not only the GNU libc. */
__closedir (dir);
int nullfd = __open_nocancel (_PATH_DEVNULL, O_RDONLY);
assert (nullfd == STDIN_FILENO);
nullfd = __open_nocancel (_PATH_DEVNULL, O_WRONLY);
assert (nullfd == STDOUT_FILENO);
__dup2 (STDOUT_FILENO, STDERR_FILENO);
}
/* Verify that fd refers to a ptmx descriptor. */
unsigned int ptyno;
int ret = __ioctl (fd, TIOCGPTN, &ptyno);
if (ret != 0 && errno == ENOTTY)
/* POSIX requires EINVAL instead of ENOTTY provided by the kernel. */
__set_errno (EINVAL);
return ret;
}
# define CLOSE_ALL_FDS() close_all_fds()
#endif
#include <sysdeps/unix/grantpt.c>

95
sysdeps/unix/sysv/linux/ptsname.c
View File

@ -21,39 +21,14 @@
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <termios.h>
#include <unistd.h>
#include <_itoa.h>
/* Check if DEV corresponds to a master pseudo terminal device. */
#define MASTER_P(Dev) \
(__gnu_dev_major ((Dev)) == 2 \
|| (__gnu_dev_major ((Dev)) == 4 \
&& __gnu_dev_minor ((Dev)) >= 128 && __gnu_dev_minor ((Dev)) < 192) \
|| (__gnu_dev_major ((Dev)) >= 128 && __gnu_dev_major ((Dev)) < 136))
/* Check if DEV corresponds to a slave pseudo terminal device. */
#define SLAVE_P(Dev) \
(__gnu_dev_major ((Dev)) == 3 \
|| (__gnu_dev_major ((Dev)) == 4 \
&& __gnu_dev_minor ((Dev)) >= 192 && __gnu_dev_minor ((Dev)) < 256) \
|| (__gnu_dev_major ((Dev)) >= 136 && __gnu_dev_major ((Dev)) < 144))
/* Note that major number 4 corresponds to the old BSD style pseudo
terminal devices. As of Linux 2.1.115 these are no longer
supported. They have been replaced by major numbers 2 (masters)
and 3 (slaves). */
/* Directory where we can find the slave pty nodes. */
#define _PATH_DEVPTS "/dev/pts/"
/* The are declared in getpt.c. */
extern const char __libc_ptyname1[] attribute_hidden;
extern const char __libc_ptyname2[] attribute_hidden;
/* Static buffer for `ptsname'. */
static char buffer[sizeof (_PATH_DEVPTS) + 20];
@ -68,19 +43,15 @@ ptsname (int fd)
}
/* Store at most BUFLEN characters of the pathname of the slave pseudo
terminal associated with the master FD is open on in BUF.
Return 0 on success, otherwise an error number. */
int
__ptsname_internal (int fd, char *buf, size_t buflen, struct stat64 *stp)
__ptsname_r (int fd, char *buf, size_t buflen)
{
int save_errno = errno;
unsigned int ptyno;
if (!__isatty (fd))
{
__set_errno (ENOTTY);
return ENOTTY;
}
#ifdef TIOCGPTN
if (__ioctl (fd, TIOCGPTN, &ptyno) == 0)
{
/* Buffer we use to print the number in. For a maximum size for
@ -101,67 +72,11 @@ __ptsname_internal (int fd, char *buf, size_t buflen, struct stat64 *stp)
memcpy (__stpcpy (buf, devpts), p, &numbuf[sizeof (numbuf)] - p);
}
else if (errno != EINVAL)
return errno;
else
#endif
{
char *p;
if (buflen < strlen (_PATH_TTY) + 3)
{
__set_errno (ERANGE);
return ERANGE;
}
if (__fstat64 (fd, stp) < 0)
return errno;
/* Check if FD really is a master pseudo terminal. */
if (! MASTER_P (stp->st_rdev))
{
__set_errno (ENOTTY);
return ENOTTY;
}
ptyno = __gnu_dev_minor (stp->st_rdev);
if (ptyno / 16 >= strlen (__libc_ptyname1))
{
__set_errno (ENOTTY);
return ENOTTY;
}
p = __stpcpy (buf, _PATH_TTY);
p[0] = __libc_ptyname1[ptyno / 16];
p[1] = __libc_ptyname2[ptyno % 16];
p[2] = '\0';
}
if (__stat64 (buf, stp) < 0)
/* Bad file descriptor, or not a ptmx descriptor. */
return errno;
/* Check if the name we're about to return really corresponds to a
slave pseudo terminal. */
if (! S_ISCHR (stp->st_mode) || ! SLAVE_P (stp->st_rdev))
{
/* This really is a configuration problem. */
__set_errno (ENOTTY);
return ENOTTY;
}
__set_errno (save_errno);
return 0;
}
/* Store at most BUFLEN characters of the pathname of the slave pseudo
terminal associated with the master FD is open on in BUF.
Return 0 on success, otherwise an error number. */
int
__ptsname_r (int fd, char *buf, size_t buflen)
{
struct stat64 st;
return __ptsname_internal (fd, buf, buflen, &st);
}
weak_alias (__ptsname_r, ptsname_r)