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Copy pathsafe_openat.c
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333 lines (283 loc) · 9.08 KB
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/*
* This code was copied from:
*
* crun - OCI runtime written in C
*
* Copyright (C) 2017, 2018, 2019 Giuseppe Scrivano <giuseppe@scrivano.org>
* crun 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.
*
* crun 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 crun. If not, see <http://www.gnu.org/licenses/>.
*/
#include "config.h"
#include "utils.h"
#include <sys/syscall.h>
#include <limits.h>
#include <unistd.h>
#include <errno.h>
#include <stdint.h>
#ifndef __set_errno
#define __set_errno(val) ((errno) = (val))
#endif
bool opt_force_openat_fallback = false;
#if ASSUMED_KERNEL < BWRAP_KERNEL_VERSION (5, 6, 0)
# define USE_OPENAT_FALLBACK 1
#else
# define USE_OPENAT_FALLBACK 0
#endif
#define cleanup_close cleanup_fd
#define LIKELY(x) __builtin_expect ((x), 1)
#define UNLIKELY(x) __builtin_expect ((x), 0)
/* Adapted from systemd. Include space for the NUL byte. */
#define DECIMAL_STR_MAX(type) \
((size_t) 2U + (sizeof (type) <= 1 ? 3U : sizeof (type) <= 2 ? 5U \
: sizeof (type) <= 4 ? 10U \
: sizeof (type) <= 8 ? 20U \
: sizeof (int[-2 * (sizeof (type) > 8)])))
#define _STRLEN(s) (sizeof (s) - 1)
/* openat2 resolve flags */
#ifndef RESOLVE_IN_ROOT
# define RESOLVE_IN_ROOT 0x10
#endif
#ifndef RESOLVE_NO_MAGICLINKS
# define RESOLVE_NO_MAGICLINKS 0x02
#endif
/* Structures for syscalls */
struct openat2_open_how
{
uint64_t flags;
uint64_t mode;
uint64_t resolve;
};
static inline int
syscall_openat2 (int dirfd, const char *path, uint64_t flags, uint64_t mode, uint64_t resolve)
{
#ifdef __NR_openat2
struct openat2_open_how how = {
.flags = flags,
.mode = mode,
.resolve = resolve,
};
return (int) syscall (__NR_openat2, dirfd, path, &how, sizeof (how), 0);
#else
(void) dirfd;
(void) path;
(void) flags;
(void) mode;
(void) resolve;
errno = ENOSYS;
return -1;
#endif
}
#define consume_slashes(t) \
({ \
__typeof__ (t) _s = (t); \
while (*_s == '/') \
_s++; \
_s; \
})
/* _STRLEN("self") < DECIMAL_STR_MAX (pid_t), so we don't need to calculate the length of both. */
#define PROC_PID_FD_STRLEN (_STRLEN ("/proc/") + DECIMAL_STR_MAX (pid_t) \
+ _STRLEN ("/fd/") + DECIMAL_STR_MAX (int))
/* A buffer long enough to hold either /proc/self/fd/$FD or a /proc/$PID/fd/$FD path. */
typedef char proc_fd_path_t[PROC_PID_FD_STRLEN];
static inline void
get_proc_fd_path (proc_fd_path_t path, pid_t pid, int fd)
{
const size_t max_len = sizeof (proc_fd_path_t);
size_t n;
if (pid)
n = snprintf (path, max_len, "/proc/%d/fd/%d", pid, fd);
else
n = snprintf (path, max_len, "/proc/self/fd/%d", fd);
if (UNLIKELY (n >= max_len))
abort ();
}
static inline void
get_proc_self_fd_path (proc_fd_path_t path, int fd)
{
get_proc_fd_path (path, 0, fd);
}
static int
check_fd_is_path (const char *path, int fd, UNUSED const char *fdname)
{
proc_fd_path_t fdpath;
size_t path_len = strlen (path);
char link[PATH_MAX];
int ret;
get_proc_self_fd_path (fdpath, fd);
ret = TEMP_FAILURE_RETRY (readlink (fdpath, link, sizeof (link)));
if (UNLIKELY (ret < 0))
return -1;
if (((size_t) ret) != path_len || memcmp (link, path, path_len))
{
// crun_make_error (err, 0, "target `%s` does not point to the directory `%s`", fdname, path);
__set_errno(ENOTDIR);
return -1;
}
return 0;
}
#if USE_OPENAT_FALLBACK
static int
check_fd_under_path (const char *rootfs, size_t rootfslen, int fd, UNUSED const char *fdname)
{
proc_fd_path_t fdpath;
char link[PATH_MAX];
int ret;
/* Every path is under "/", there is nothing to verify. The check below
would reject any path since it expects a '/' right after the rootfs. */
if (rootfslen == 0 || (rootfslen == 1 && rootfs[0] == '/'))
return 0;
get_proc_self_fd_path (fdpath, fd);
ret = TEMP_FAILURE_RETRY (readlink (fdpath, link, sizeof (link)));
if (UNLIKELY (ret < 0))
return -1;
if (((size_t) ret) <= rootfslen || memcmp (link, rootfs, rootfslen) != 0 || link[rootfslen] != '/')
{
// crun_make_error (err, 0, "target `%s` not under the directory `%s`", fdname, rootfs);
__set_errno(ENOTDIR);
return -1;
}
return 0;
}
#endif
/* DIRFD must be a file descriptor for ROOTFS itself: PATH is resolved
against ROOTFS and the result is then opened relatively to DIRFD. */
static int
safe_openat_fallback (int dirfd, const char *rootfs, const char *path, int flags,
int mode)
{
#if !USE_OPENAT_FALLBACK
(void) dirfd;
(void) rootfs;
(void) path;
(void) flags;
(void) mode;
errno = ENOSYS;
return -1;
#else
cleanup_free char *parent_path = NULL;
const char *last_component = NULL;
const char *orig_path = path;
const char *path_in_chroot;
cleanup_close int fd = -1;
char resolved[PATH_MAX];
char buffer[PATH_MAX];
size_t rootfs_len = is_empty_string (rootfs) ? 0 : strlen (rootfs);
int ret;
/* chroot_realpath resolves the last component as well, so when O_NOFOLLOW
is requested resolve only the parent directory and let openat(2) deal
with the last component, otherwise a symlink would be followed even
though the caller asked not to. */
if (flags & O_NOFOLLOW)
{
char *sep;
parent_path = xstrdup (path);
sep = strrchr (parent_path, '/');
if (sep == NULL)
{
/* No parent directory, the entire path is the last component. */
last_component = path;
parent_path[0] = '\0';
}
else if (sep[1] != '\0')
{
*sep = '\0';
last_component = path + (sep - parent_path) + 1;
}
/* A trailing '/' forces the symlink to be resolved anyway, so in that
case keep resolving the entire path. */
if (last_component)
path = parent_path;
}
path_in_chroot = chroot_realpath (rootfs, path, buffer);
if (path_in_chroot == NULL)
return -1;
/* When rootfs is "/" or not set, chroot_realpath returns the path
unchanged, so drop the prefix only when it is really there. */
if (rootfs_len > 0 && strncmp (path_in_chroot, rootfs, rootfs_len) == 0)
path_in_chroot += rootfs_len;
path_in_chroot = consume_slashes (path_in_chroot);
if (last_component)
{
ret = snprintf (resolved, sizeof (resolved), "%s%s%s", path_in_chroot,
path_in_chroot[0] == '\0' ? "" : "/", last_component);
if (UNLIKELY (ret >= (int) sizeof (resolved)))
{
__set_errno (ENAMETOOLONG);
return -1;
}
path_in_chroot = resolved;
}
/* If the path is empty we are at the root, dup the dirfd itself. */
if (path_in_chroot[0] == '\0')
{
ret = dup (dirfd);
if (UNLIKELY (ret < 0))
return -1;
return ret;
}
ret = openat (dirfd, path_in_chroot, flags, mode);
if (UNLIKELY (ret < 0))
return -1;
fd = ret;
ret = check_fd_under_path (rootfs, rootfs_len, fd, orig_path);
if (UNLIKELY (ret < 0))
return ret;
ret = fd;
fd = -1;
return ret;
#endif /* USE_OPENAT_FALLBACK */
}
int
safe_openat (int dirfd, const char *rootfs, const char *path, int flags, int mode)
{
static bool openat2_supported = true;
int ret;
if (is_empty_string (path))
{
cleanup_close int fd = -1;
fd = open (rootfs, flags, mode);
if (UNLIKELY (fd < 0))
return -1;
/* Skip the readlink-based check when opening the root
directory itself (rootfs="/", path=""). After pivot_root,
"/" can only refer to the container root so the readlink
verification is redundant, and after setns the /proc-based
readlink may not be reachable by path yet. */
if (rootfs[0] != '/' || rootfs[1] != '\0')
{
ret = check_fd_is_path (rootfs, fd, path);
if (UNLIKELY (ret < 0))
return ret;
}
ret = fd;
fd = -1;
return ret;
}
if (openat2_supported && !opt_force_openat_fallback)
{
repeat:
ret = syscall_openat2 (dirfd, path, flags, mode, RESOLVE_IN_ROOT|RESOLVE_NO_MAGICLINKS);
if (UNLIKELY (ret < 0))
{
if (errno == EINTR || errno == EAGAIN)
goto repeat;
if (errno == ENOSYS)
openat2_supported = false;
if (errno == ENOSYS || errno == EINVAL || errno == EPERM)
return safe_openat_fallback (dirfd, rootfs, path, flags, mode);
return -1;
}
return ret;
}
return safe_openat_fallback (dirfd, rootfs, path, flags, mode);
}
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