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/*
* Copyright (c) 2020-2021 The strace developers.
* All rights reserved.
*
* SPDX-License-Identifier: LGPL-2.1-or-later
*/
#include "defs.h"
#include <stdlib.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/stat.h>
#include <unistd.h>
#include <selinux/selinux.h>
#include <selinux/label.h>
#include "largefile_wrappers.h"
#include "number_set.h"
#include "secontext.h"
#include "xmalloc.h"
#include "xstring.h"
static int
getcontext(int rc, char **secontext, char **result)
{
if (rc < 0)
return rc;
*result = NULL;
if (!is_number_in_set(SECONTEXT_FULL, secontext_set)) {
char *saveptr = NULL;
char *secontext_copy = xstrdup(*secontext);
const char *token;
unsigned int i;
/*
* We only want to keep the type (3rd field, ':' separator).
*/
for (token = strtok_r(secontext_copy, ":", &saveptr), i = 0;
token; token = strtok_r(NULL, ":", &saveptr), i++) {
if (i == 2) {
*result = xstrdup(token);
break;
}
}
free(secontext_copy);
}
if (*result == NULL) {
/*
* On the CI at least, the context may have a trailing \n,
* let's remove it just in case.
*/
size_t len = strlen(*secontext);
for (; len > 0; --len) {
if ((*secontext)[len - 1] != '\n')
break;
}
*result = xstrndup(*secontext, len);
}
freecon(*secontext);
return 0;
}
static int
get_expected_filecontext(const char *path, char **result)
{
static struct selabel_handle *hdl;
if (!hdl) {
static bool disabled;
if (disabled)
return -1;
hdl = selabel_open(SELABEL_CTX_FILE, NULL, 0);
if (!hdl) {
perror_msg("could not open SELinux database, disabling "
"context mismatch checking");
disabled = true;
return -1;
}
}
strace_stat_t stb;
if (stat_file(path, &stb) < 0) {
return -1;
}
char *secontext;
return getcontext(selabel_lookup(hdl, &secontext, path, stb.st_mode),
&secontext, result);
}
/*
* Retrieves the SELinux context of the given PID (extracted from the tcb).
* Memory must be freed.
* Returns 0 on success, -1 on failure.
*/
int
selinux_getpidcon(struct tcb *tcp, char **result)
{
if (number_set_array_is_empty(secontext_set, 0))
return -1;
int proc_pid = get_proc_pid(tcp->pid);
if (!proc_pid)
return -1;
char *secontext;
return getcontext(getpidcon(proc_pid, &secontext), &secontext, result);
}
/*
* Retrieves the SELinux context of the given pid and descriptor.
* Memory must be freed.
* Returns 0 on success, -1 on failure.
*/
int
selinux_getfdcon(pid_t pid, int fd, char **result)
{
if (number_set_array_is_empty(secontext_set, 0) || pid <= 0 || fd < 0)
return -1;
int proc_pid = get_proc_pid(pid);
if (!proc_pid)
return -1;
char linkpath[sizeof("/proc/%u/fd/%u") + 2 * sizeof(int)*3];
xsprintf(linkpath, "/proc/%u/fd/%u", proc_pid, fd);
char *secontext;
int rc = getcontext(getfilecon(linkpath, &secontext), &secontext, result);
if (rc < 0 || !is_number_in_set(SECONTEXT_MISMATCH, secontext_set))
return rc;
/*
* We need to resolve the path, because selabel_lookup() doesn't
* resolve anything. Using readlink() is sufficient here.
*/
char buf[PATH_MAX];
ssize_t n = readlink(linkpath, buf, sizeof(buf));
if ((size_t) n >= sizeof(buf))
return 0;
buf[n] = '\0';
char *expected;
if (get_expected_filecontext(buf, &expected) < 0)
return 0;
if (strcmp(expected, *result) == 0) {
free(expected);
return 0;
}
char *final_result = xasprintf("%s!!%s", *result, expected);
free(expected);
free(*result);
*result = final_result;
return 0;
}
/*
* Retrieves the SELinux context of the given path.
* Memory must be freed.
* Returns 0 on success, -1 on failure.
*/
int
selinux_getfilecon(struct tcb *tcp, const char *path, char **result)
{
if (number_set_array_is_empty(secontext_set, 0))
return -1;
int proc_pid = get_proc_pid(tcp->pid);
if (!proc_pid)
return -1;
int rc = -1;
char fname[PATH_MAX];
if (path[0] == '/')
rc = snprintf(fname, sizeof(fname), "/proc/%u/root%s",
proc_pid, path);
else if (tcp->last_dirfd == AT_FDCWD)
rc = snprintf(fname, sizeof(fname), "/proc/%u/cwd/%s",
proc_pid, path);
else if (tcp->last_dirfd >= 0 )
rc = snprintf(fname, sizeof(fname), "/proc/%u/fd/%u/%s",
proc_pid, tcp->last_dirfd, path);
if ((unsigned int) rc >= sizeof(fname))
return -1;
char *secontext;
rc = getcontext(getfilecon(fname, &secontext), &secontext, result);
if (rc < 0 || !is_number_in_set(SECONTEXT_MISMATCH, secontext_set))
return rc;
/*
* We need to fully resolve the path, because selabel_lookup() doesn't
* resolve anything. Using realpath() is the only solution here to make
* sure the path is canonicalized.
*/
char *resolved = realpath(fname, NULL);
if (!resolved)
return 0;
char *expected;
rc = get_expected_filecontext(resolved, &expected);
free(resolved);
if (rc < 0)
return 0;
if (strcmp(expected, *result) == 0) {
free(expected);
return 0;
}
char *final_result = xasprintf("%s!!%s", *result, expected);
free(expected);
free(*result);
*result = final_result;
return 0;
}
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