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Move safe open code out of sudo_edit.c and into edit_open.c.

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This commit is contained in:
Todd C. Miller
2021-01-06 13:01:09 -07:00
parent 397a07e86f
commit a5be62c68f
7 changed files with 497 additions and 407 deletions
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398
src/sudo_edit.c
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@@ -31,7 +31,6 @@
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <ctype.h>
#include <errno.h>
#include <grp.h>
#include <pwd.h>
@@ -39,6 +38,7 @@
#include <fcntl.h>
#include "sudo.h"
#include "sudo_edit.h"
#include "sudo_exec.h"
#if defined(HAVE_SETRESUID) || defined(HAVE_SETREUID) || defined(HAVE_SETEUID)
@@ -55,146 +55,6 @@ struct tempfile {
static char edit_tmpdir[MAX(sizeof(_PATH_VARTMP), sizeof(_PATH_TMP))];
static void
switch_user(uid_t euid, gid_t egid, int ngroups, GETGROUPS_T *groups)
{
int serrno = errno;
debug_decl(switch_user, SUDO_DEBUG_EDIT);
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"set uid:gid to %u:%u(%u)", (unsigned int)euid, (unsigned int)egid,
ngroups ? (unsigned int)groups[0] : (unsigned int)egid);
/* When restoring root, change euid first; otherwise change it last. */
if (euid == ROOT_UID) {
if (seteuid(ROOT_UID) != 0)
sudo_fatal("seteuid(ROOT_UID)");
}
if (setegid(egid) != 0)
sudo_fatal("setegid(%d)", (int)egid);
if (ngroups != -1) {
if (sudo_setgroups(ngroups, groups) != 0)
sudo_fatal("setgroups");
}
if (euid != ROOT_UID) {
if (seteuid(euid) != 0)
sudo_fatal("seteuid(%u)", (unsigned int)euid);
}
errno = serrno;
debug_return;
}
#if defined(HAVE_FACCESSAT) && defined(AT_EACCESS)
/*
* Returns true if the open directory fd is owned or writable by the user.
*/
static int
dir_is_writable(int dfd, struct user_details *ud, struct command_details *cd)
{
struct stat sb;
int rc;
debug_decl(dir_is_writable, SUDO_DEBUG_EDIT);
if (fstat(dfd, &sb) == -1)
debug_return_int(-1);
/* If the user owns the dir we always consider it writable. */
if (sb.st_uid == ud->uid) {
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"user uid %u matches directory uid %u", (unsigned int)ud->uid,
(unsigned int)sb.st_uid);
debug_return_int(true);
}
/* Change uid/gid/groups to invoking user, usually needs root perms. */
if (cd->euid != ROOT_UID) {
if (seteuid(ROOT_UID) != 0)
sudo_fatal("seteuid(ROOT_UID)");
}
switch_user(ud->uid, ud->gid, ud->ngroups, ud->groups);
/* Access checks are done using the euid/egid and group vector. */
rc = faccessat(dfd, ".", W_OK, AT_EACCESS);
/* Change uid/gid/groups back to target user, may need root perms. */
if (ud->uid != ROOT_UID) {
if (seteuid(ROOT_UID) != 0)
sudo_fatal("seteuid(ROOT_UID)");
}
switch_user(cd->euid, cd->egid, cd->ngroups, cd->groups);
if (rc == 0)
debug_return_int(true);
if (errno == EACCES || errno == EROFS)
debug_return_int(false);
debug_return_int(-1);
}
#else
static bool
group_matches(gid_t target, gid_t gid, int ngroups, GETGROUPS_T *groups)
{
int i;
debug_decl(group_matches, SUDO_DEBUG_EDIT);
if (target == gid) {
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"user gid %u matches directory gid %u", (unsigned int)gid,
(unsigned int)target);
debug_return_bool(true);
}
for (i = 0; i < ngroups; i++) {
if (target == groups[i]) {
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"user gid %u matches directory gid %u", (unsigned int)gid,
(unsigned int)target);
debug_return_bool(true);
}
}
debug_return_bool(false);
}
/*
* Returns true if the open directory fd is owned or writable by the user.
*/
static int
dir_is_writable(int dfd, struct user_details *ud, struct command_details *cd)
{
struct stat sb;
debug_decl(dir_is_writable, SUDO_DEBUG_EDIT);
if (fstat(dfd, &sb) == -1)
debug_return_int(-1);
/* If the user owns the dir we always consider it writable. */
if (sb.st_uid == ud->uid) {
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"user uid %u matches directory uid %u", (unsigned int)ud->uid,
(unsigned int)sb.st_uid);
debug_return_int(true);
}
/* Other writable? */
if (ISSET(sb.st_mode, S_IWOTH)) {
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"directory is writable by other");
debug_return_int(true);
}
/* Group writable? */
if (ISSET(sb.st_mode, S_IWGRP)) {
if (group_matches(sb.st_gid, ud->gid, ud->ngroups, ud->groups)) {
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"directory is writable by one of the user's groups");
debug_return_int(true);
}
}
errno = EACCES;
debug_return_int(false);
}
#endif /* HAVE_FACCESSAT && AT_EACCESS */
/*
* Find our temporary directory, one of /var/tmp, /usr/tmp, or /tmp
* Returns true on success, else false;
@@ -269,253 +129,6 @@ sudo_edit_mktemp(const char *ofile, char **tfile)
debug_return_int(tfd);
}
#ifdef O_NOFOLLOW
static int
sudo_edit_openat_nofollow(int dfd, char *path, int oflags, mode_t mode)
{
debug_decl(sudo_edit_openat_nofollow, SUDO_DEBUG_EDIT);
debug_return_int(openat(dfd, path, oflags|O_NOFOLLOW, mode));
}
#else
/*
* Returns true if fd and path don't match or path is a symlink.
* Used on older systems without O_NOFOLLOW.
*/
static bool
sudo_edit_is_symlink(int fd, char *path)
{
struct stat sb1, sb2;
debug_decl(sudo_edit_is_symlink, SUDO_DEBUG_EDIT);
/*
* Treat [fl]stat() failure like there was a symlink.
*/
if (fstat(fd, &sb1) == -1 || lstat(path, &sb2) == -1)
debug_return_bool(true);
/*
* Make sure we did not open a link and that what we opened
* matches what is currently on the file system.
*/
if (S_ISLNK(sb2.st_mode) ||
sb1.st_dev != sb2.st_dev || sb1.st_ino != sb2.st_ino) {
debug_return_bool(true);
}
debug_return_bool(false);
}
static int
sudo_edit_openat_nofollow(int dfd, char *path, int oflags, mode_t mode)
{
int fd = -1, odfd = -1;
struct stat sb;
debug_decl(sudo_edit_openat_nofollow, SUDO_DEBUG_EDIT);
/* Save cwd and chdir to dfd */
if ((odfd = open(".", O_RDONLY)) == -1)
debug_return_int(-1);
if (fchdir(dfd) == -1) {
close(odfd);
debug_return_int(-1);
}
/*
* Check if path is a symlink. This is racey but we detect whether
* we lost the race in sudo_edit_is_symlink() after the open.
*/
if (lstat(path, &sb) == -1 && errno != ENOENT)
goto done;
if (S_ISLNK(sb.st_mode)) {
errno = ELOOP;
goto done;
}
fd = open(path, oflags, mode);
if (fd == -1)
goto done;
/*
* Post-open symlink check. This will leave a zero-length file if
* O_CREAT was specified but it is too dangerous to try and remove it.
*/
if (sudo_edit_is_symlink(fd, path)) {
close(fd);
fd = -1;
errno = ELOOP;
}
done:
/* Restore cwd */
if (odfd != -1) {
if (fchdir(odfd) == -1)
sudo_fatal("%s", U_("unable to restore current working directory"));
close(odfd);
}
debug_return_int(fd);
}
#endif /* O_NOFOLLOW */
/*
* Directory open flags for use with openat(2).
* Use O_SEARCH/O_PATH and/or O_DIRECTORY where possible.
*/
#if defined(O_SEARCH)
# if defined(O_DIRECTORY)
# define DIR_OPEN_FLAGS (O_SEARCH|O_DIRECTORY)
# else
# define DIR_OPEN_FLAGS (O_SEARCH)
# endif
#elif defined(O_PATH)
# if defined(O_DIRECTORY)
# define DIR_OPEN_FLAGS (O_PATH|O_DIRECTORY)
# else
# define DIR_OPEN_FLAGS (O_PATH)
# endif
#elif defined(O_DIRECTORY)
# define DIR_OPEN_FLAGS (O_RDONLY|O_DIRECTORY)
#else
# define DIR_OPEN_FLAGS (O_RDONLY|O_NONBLOCK)
#endif
static int
sudo_edit_open_nonwritable(char *path, int oflags, mode_t mode,
struct command_details *command_details)
{
const int dflags = DIR_OPEN_FLAGS;
int dfd, fd, is_writable;
debug_decl(sudo_edit_open_nonwritable, SUDO_DEBUG_EDIT);
if (path[0] == '/') {
dfd = open("/", dflags);
path++;
} else {
dfd = open(".", dflags);
if (path[0] == '.' && path[1] == '/')
path += 2;
}
if (dfd == -1)
debug_return_int(-1);
for (;;) {
char *slash;
int subdfd;
/*
* Look up one component at a time, avoiding symbolic links in
* writable directories.
*/
is_writable = dir_is_writable(dfd, &user_details, command_details);
if (is_writable == -1) {
close(dfd);
debug_return_int(-1);
}
while (path[0] == '/')
path++;
slash = strchr(path, '/');
if (slash == NULL)
break;
*slash = '\0';
if (is_writable)
subdfd = sudo_edit_openat_nofollow(dfd, path, dflags, 0);
else
subdfd = openat(dfd, path, dflags, 0);
*slash = '/'; /* restore path */
close(dfd);
if (subdfd == -1)
debug_return_int(-1);
path = slash + 1;
dfd = subdfd;
}
if (is_writable) {
close(dfd);
errno = EISDIR;
debug_return_int(-1);
}
/*
* For "sudoedit /" we will receive ENOENT from openat() and sudoedit
* will try to create a file with an empty name. We treat an empty
* path as the cwd so sudoedit can give a sensible error message.
*/
fd = openat(dfd, *path ? path : ".", oflags, mode);
close(dfd);
debug_return_int(fd);
}
#ifdef O_NOFOLLOW
static int
sudo_edit_open(char *path, int oflags, mode_t mode,
struct command_details *command_details)
{
const int sflags = command_details ? command_details->flags : 0;
int fd;
debug_decl(sudo_edit_open, SUDO_DEBUG_EDIT);
if (!ISSET(sflags, CD_SUDOEDIT_FOLLOW))
oflags |= O_NOFOLLOW;
if (ISSET(sflags, CD_SUDOEDIT_CHECKDIR) && user_details.uid != ROOT_UID) {
fd = sudo_edit_open_nonwritable(path, oflags|O_NONBLOCK, mode,
command_details);
} else {
fd = open(path, oflags|O_NONBLOCK, mode);
}
if (fd != -1 && !ISSET(oflags, O_NONBLOCK))
(void) fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) & ~O_NONBLOCK);
debug_return_int(fd);
}
#else
static int
sudo_edit_open(char *path, int oflags, mode_t mode,
struct command_details *command_details)
{
const int sflags = command_details ? command_details->flags : 0;
struct stat sb;
int fd;
debug_decl(sudo_edit_open, SUDO_DEBUG_EDIT);
/*
* Check if path is a symlink. This is racey but we detect whether
* we lost the race in sudo_edit_is_symlink() after the file is opened.
*/
if (!ISSET(sflags, CD_SUDOEDIT_FOLLOW)) {
if (lstat(path, &sb) == -1 && errno != ENOENT)
debug_return_int(-1);
if (S_ISLNK(sb.st_mode)) {
errno = ELOOP;
debug_return_int(-1);
}
}
if (ISSET(sflags, CD_SUDOEDIT_CHECKDIR) && user_details.uid != ROOT_UID) {
fd = sudo_edit_open_nonwritable(path, oflags|O_NONBLOCK, mode,
command_details);
} else {
fd = open(path, oflags|O_NONBLOCK, mode);
}
if (fd == -1)
debug_return_int(-1);
if (!ISSET(oflags, O_NONBLOCK))
(void) fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) & ~O_NONBLOCK);
/*
* Post-open symlink check. This will leave a zero-length file if
* O_CREAT was specified but it is too dangerous to try and remove it.
*/
if (!ISSET(sflags, CD_SUDOEDIT_FOLLOW) && sudo_edit_is_symlink(fd, path)) {
close(fd);
fd = -1;
errno = ELOOP;
}
debug_return_int(fd);
}
#endif /* O_NOFOLLOW */
/*
* Create temporary copies of files[] and store the temporary path name
* along with the original name, size and mtime in tf.
@@ -540,7 +153,7 @@ sudo_edit_create_tfiles(struct command_details *command_details,
switch_user(command_details->euid, command_details->egid,
command_details->ngroups, command_details->groups);
ofd = sudo_edit_open(files[i], O_RDONLY,
S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH, command_details);
S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH, &user_details, command_details);
if (ofd != -1 || errno == ENOENT) {
if (ofd == -1) {
/*
@@ -562,7 +175,8 @@ sudo_edit_create_tfiles(struct command_details *command_details,
*slash = '\0';
SET(command_details->flags, CD_SUDOEDIT_FOLLOW);
dfd = sudo_edit_open(files[i], DIR_OPEN_FLAGS,
S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH, command_details);
S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH, &user_details,
command_details);
command_details->flags = sflags;
if (dfd != -1) {
if (fstat(dfd, &sb) == 0 && S_ISDIR(sb.st_mode)) {
@@ -672,7 +286,7 @@ sudo_edit_copy_tfiles(struct command_details *command_details,
if (seteuid(user_details.uid) != 0)
sudo_fatal("seteuid(%u)", (unsigned int)user_details.uid);
tfd = sudo_edit_open(tf[i].tfile, O_RDONLY,
S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH, NULL);
S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH, &user_details, NULL);
if (seteuid(ROOT_UID) != 0)
sudo_fatal("seteuid(ROOT_UID)");
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
@@ -701,7 +315,7 @@ sudo_edit_copy_tfiles(struct command_details *command_details,
command_details->ngroups, command_details->groups);
oldmask = umask(command_details->umask);
ofd = sudo_edit_open(tf[i].ofile, O_WRONLY|O_CREAT,
S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH, command_details);
S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH, &user_details, command_details);
umask(oldmask);
switch_user(ROOT_UID, user_details.egid,
user_details.ngroups, user_details.groups);