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Implement sudo_intercept.so.

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Uses protobuf to talk to main sudo process over a socketpair.
This commit is contained in:
Todd C. Miller
2021-08-09 15:50:25 -06:00
parent d7380bb271
commit 4cf3d1c416
7 changed files with 631 additions and 96 deletions
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2
MANIFEST
View File

@@ -1129,6 +1129,8 @@ src/sudo.h
src/sudo_edit.c
src/sudo_edit.h
src/sudo_exec.h
src/sudo_intercept.c
src/sudo_intercept_common.c
src/sudo_noexec.c
src/sudo_plugin_int.h
src/sudo_usage.h.in

31
src/Makefile.in
View File

@@ -102,6 +102,8 @@ libexecdir = @libexecdir@
datarootdir = @datarootdir@
localedir = @localedir@
localstatedir = @localstatedir@
interceptfile = @INTERCEPTFILE@
interceptdir = @INTERCEPTDIR@
noexecfile = @NOEXECFILE@
noexecdir = @NOEXECDIR@
tmpfiles_d = @TMPFILES_D@
@@ -199,6 +201,9 @@ $(devdir)/intercept.pb-c.c: $(srcdir)/intercept.proto
sudo: $(OBJS) $(LT_LIBS) @STATIC_SUDOERS@
$(LIBTOOL) $(LTFLAGS) --mode=link $(CC) -o $@ $(OBJS) $(SUDO_LDFLAGS) $(ASAN_LDFLAGS) $(PIE_LDFLAGS) $(SSP_LDFLAGS) $(LIBS) @STATIC_SUDOERS@
sudo_intercept.la: sudo_intercept.lo sudo_intercept_common.lo intercept.pb-c.lo
$(LIBTOOL) $(LTFLAGS) --mode=link $(CC) $(LDFLAGS) $(LT_LDFLAGS) $(SSP_LDFLAGS) $(LT_LIBS) @LIBDL@ -o $@ sudo_intercept.lo sudo_intercept_common.lo intercept.pb-c.lo $(PRELOAD_MODULE) -avoid-version -rpath $(interceptdir) -shrext .so
sudo_noexec.la: sudo_noexec.lo
$(LIBTOOL) $(LTFLAGS) --mode=link $(CC) $(LDFLAGS) $(LT_LDFLAGS) $(SSP_LDFLAGS) @LIBDL@ -o $@ sudo_noexec.lo $(PRELOAD_MODULE) -avoid-version -rpath $(noexecdir) -shrext .so
@@ -216,12 +221,13 @@ check_ttyname: $(CHECK_TTYNAME_OBJS) $(top_builddir)/lib/util/libsudo_util.la
pre-install:
install: install-binaries install-rc @INSTALL_NOEXEC@
install: install-binaries install-rc @INSTALL_INTERCEPT@ @INSTALL_NOEXEC@
install-dirs:
# We only create the rc.d dir when installing to the actual system dir
$(SHELL) $(scriptdir)/mkinstalldirs $(DESTDIR)$(bindir) \
$(DESTDIR)$(libexecdir)/sudo $(DESTDIR)$(noexecdir)
$(DESTDIR)$(libexecdir)/sudo $(DESTDIR)$(noexecdir) \
$(DESTDIR)$(interceptdir)
if test -n "$(INIT_SCRIPT)"; then \
$(SHELL) $(scriptdir)/mkinstalldirs $(DESTDIR)$(INIT_DIR); \
if test -z "$(DESTDIR)"; then \
@@ -256,6 +262,9 @@ install-doc:
install-includes:
install-intercept: install-dirs sudo_intercept.la
INSTALL_BACKUP='$(INSTALL_BACKUP)' $(LIBTOOL) $(LTFLAGS) --mode=install $(INSTALL) $(INSTALL_OWNER) -m $(shlib_mode) sudo_intercept.la $(DESTDIR)$(interceptdir)
install-noexec: install-dirs sudo_noexec.la
INSTALL_BACKUP='$(INSTALL_BACKUP)' $(LIBTOOL) $(LTFLAGS) --mode=install $(INSTALL) $(INSTALL_OWNER) -m $(shlib_mode) sudo_noexec.la $(DESTDIR)$(noexecdir)
@@ -265,7 +274,8 @@ install-fuzzer:
uninstall:
-$(LIBTOOL) $(LTFLAGS) --mode=uninstall \
rm -f $(DESTDIR)$(noexecdir)/sudo_noexec.la
rm -f $(DESTDIR)$(interceptdir)/sudo_intercept.la \
$(DESTDIR)$(noexecdir)/sudo_noexec.la
-rm -f $(DESTDIR)$(bindir)/sudo \
$(DESTDIR)$(bindir)/sudoedit \
$(DESTDIR)$(libexecdir)/sudo/sesh \
@@ -273,6 +283,7 @@ uninstall:
-test -z "$(INSTALL_BACKUP)" || \
rm -f $(DESTDIR)$(bindir)/sudo$(INSTALL_BACKUP) \
$(DESTDIR)$(libexecdir)/sudo/sesh$(INSTALL_BACKUP) \
$(DESTDIR)$(interceptdir)/sudo_intercept.so$(INSTALL_BACKUP) \
$(DESTDIR)$(noexecdir)/sudo_noexec.so$(INSTALL_BACKUP)
-test -z "$(INIT_SCRIPT)" || \
rm -f $(DESTDIR)$(RC_LINK) $(DESTDIR)$(INIT_DIR)/sudo
@@ -333,6 +344,20 @@ cleandir: realclean
.PHONY: clean mostlyclean distclean cleandir clobber realclean
# *Not* auto-generated to avoid building with ASAN
sudo_intercept.lo: $(srcdir)/sudo_intercept.c $(incdir)/sudo_compat.h \
$(top_builddir)/config.h $(top_builddir)/pathnames.h
$(LIBTOOL) $(LTFLAGS) --mode=compile $(CC) -c $(CPPFLAGS) $(CFLAGS) $(PIE_CFLAGS) $(SSP_CFLAGS) $(srcdir)/sudo_intercept.c
sudo_intercept_common.lo: $(srcdir)/sudo_intercept_common.c \
$(incdir)/sudo_compat.h $(incdir)/sudo_fatal.h \
$(incdir)/sudo_gettext.h $(incdir)/intercept.pb-c.h \
$(srcdir)/sudo_exec.h $(top_builddir)/config.h
$(LIBTOOL) $(LTFLAGS) --mode=compile $(CC) -c $(CPPFLAGS) $(CFLAGS) $(PIE_CFLAGS) $(SSP_CFLAGS) $(srcdir)/sudo_intercept_common.c
intercept.pb-c.lo: $(srcdir)/intercept.pb-c.c $(incdir)/intercept.pb-c.h \
$(incdir)/protobuf-c/protobuf-c.h
$(LIBTOOL) $(LTFLAGS) --mode=compile $(CC) -c $(CPPFLAGS) $(CFLAGS) $(PIE_CFLAGS) $(SSP_CFLAGS) $(srcdir)/intercept.pb-c.c
sudo_noexec.lo: $(srcdir)/sudo_noexec.c $(incdir)/sudo_compat.h \
$(top_builddir)/config.h $(top_builddir)/pathnames.h
$(LIBTOOL) $(LTFLAGS) --mode=compile $(CC) -c $(CPPFLAGS) $(CFLAGS) $(PIE_CFLAGS) $(SSP_CFLAGS) $(srcdir)/sudo_noexec.c

178
src/exec.c
View File

@@ -480,7 +480,7 @@ struct intercept_closure {
char *command; /* dynamically allocated */
char **run_argv; /* owned by plugin */
char **run_envp; /* dynamically allocated */
char *buf; /* dynamically allocated */
uint8_t *buf; /* dynamically allocated */
size_t len;
int policy_result;
};
@@ -491,16 +491,24 @@ struct intercept_closure {
static void
intercept_closure_reset(struct intercept_closure *closure)
{
size_t n;
debug_decl(intercept_closure_reset, SUDO_DEBUG_EXEC);
/* Other parts of closure are freed at policy close time. */
/* TODO: can we cause them to be freed earlier? */
free(closure->buf);
free(closure->command);
if (closure->run_argv != NULL) {
for (n = 0; closure->run_argv[n] != NULL; n++)
free(closure->run_argv[n]);
free(closure->run_argv);
}
if (closure->run_envp != NULL) {
for (n = 0; closure->run_envp[n] != NULL; n++)
free(closure->run_envp[n]);
free(closure->run_envp);
}
sudo_ev_del(NULL, &closure->ev);
/* Reset all but the event. */
/* Reset all but the event (which we may reuse). */
closure->errstr = NULL;
closure->command = NULL;
closure->run_argv = NULL;
@@ -534,7 +542,7 @@ intercept_check_policy(PolicyCheckRequest *req,
{
char **command_info = NULL;
char **user_env_out = NULL;
char **vec;
char **argv, **run_argv = NULL;
size_t n;
int ok;
debug_decl(intercept_check_policy, SUDO_DEBUG_EXEC);
@@ -554,23 +562,27 @@ intercept_check_policy(PolicyCheckRequest *req,
}
/* Rebuild argv from PolicyCheckReq so it is NULL-terminated. */
vec = reallocarray(NULL, req->n_argv + 1, sizeof(char *));
if (vec == NULL) {
argv = reallocarray(NULL, req->n_argv + 1, sizeof(char *));
if (argv == NULL) {
*errstr = N_("unable to allocate memory");
goto error;
}
for (n = 0; n < req->n_argv; n++) {
vec[n] = req->argv[n];
argv[n] = req->argv[n];
}
vec[n] = NULL;
argv[n] = NULL;
/* We don't currently have a good way to validate the environment. */
/* TODO: make sure LD_PRELOAD is preserved in environment */
sudo_debug_set_active_instance(policy_plugin.debug_instance);
ok = policy_plugin.u.policy->check_policy(n, vec, NULL,
&command_info, &closure->run_argv, &user_env_out, errstr);
ok = policy_plugin.u.policy->check_policy(n, argv, NULL,
&command_info, &run_argv, &user_env_out, errstr);
sudo_debug_set_active_instance(sudo_debug_instance);
free(vec);
free(argv);
switch (ok) {
case 1:
/* TODO: call approval plugin too */
/* Extract command path from command_info[] */
if (command_info != NULL) {
@@ -587,21 +599,46 @@ intercept_check_policy(PolicyCheckRequest *req,
}
}
switch (ok) {
case 1:
/* TODO: call approval plugin too */
if (sudo_debug_needed(SUDO_DEBUG_INFO)) {
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"run_command: %s", closure->command);
for (n = 0; run_argv[n] != NULL; n++) {
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"run_argv[%zu]: %s", n, run_argv[n]);
}
}
/* Rebuild envp from PolicyCheckReq so it is NULL-terminated. */
vec = reallocarray(NULL, req->n_envp + 1, sizeof(char *));
if (vec == NULL) {
/* run_argv strings may be part of PolicyCheckReq, make a copy. */
for (n = 0; run_argv[n] != NULL; n++)
continue;
closure->run_argv = reallocarray(NULL, n + 1, sizeof(char *));
if (closure->run_argv == NULL) {
*errstr = N_("unable to allocate memory");
goto error;
}
for (n = 0; run_argv[n] != NULL; n++) {
closure->run_argv[n] = strdup(run_argv[n]);
if (closure->run_argv[n] == NULL) {
*errstr = N_("unable to allocate memory");
goto error;
}
}
closure->run_argv[n] = NULL;
/* envp strings are part of PolicyCheckReq, make a copy. */
closure->run_envp = reallocarray(NULL, req->n_envp + 1, sizeof(char *));
if (closure->run_envp == NULL) {
*errstr = N_("unable to allocate memory");
goto error;
}
for (n = 0; n < req->n_envp; n++) {
vec[n] = req->envp[n];
closure->run_envp[n] = strdup(req->envp[n]);
if (closure->run_envp[n] == NULL) {
*errstr = N_("unable to allocate memory");
goto error;
}
vec[n] = NULL;
closure->run_envp = vec;
}
closure->run_envp[n] = NULL;
/* Audit the event twice: once for the plugin, once for sudo. */
audit_accept(policy_plugin.name, SUDO_POLICY_PLUGIN, command_info,
@@ -625,18 +662,18 @@ intercept_check_policy(PolicyCheckRequest *req,
}
}
#define MESSAGE_SIZE_MAX (2 * 1024 * 1024)
/*
* Read a single message from sudo_intercept.so.
*/
static void
static bool
intercept_read(int fd, struct intercept_closure *closure)
{
InterceptMessage *msg;
struct sudo_event_base *base = sudo_ev_get_base(&closure->ev);
InterceptMessage *msg = NULL;
uint8_t *cp, *buf = NULL;
uint32_t msg_len;
ssize_t nread;
char *buf = NULL;
bool ret = false;
debug_decl(intercept_read, SUDO_DEBUG_EXEC);
/* Read message size (uint32_t in host byte order). */
@@ -644,46 +681,49 @@ intercept_read(int fd, struct intercept_closure *closure)
if (nread != sizeof(msg_len)) {
if (nread != 0)
sudo_warn("read");
goto bad;
goto done;
}
if (msg_len > MESSAGE_SIZE_MAX) {
sudo_warnx(U_("client message too large: %zu"), (size_t)msg_len);
goto bad;
goto done;
}
if (msg_len > 0) {
size_t rem = msg_len;
if ((buf = malloc(msg_len)) == NULL) {
sudo_warnx("%s", U_("unable to allocate memory"));
goto bad;
goto done;
}
cp = buf;
do {
size_t len = MIN(msg_len, sizeof(buf));
nread = read(fd, buf, len);
nread = read(fd, cp, rem);
switch (nread) {
case 0:
/* EOF, other side must have exited. */
goto bad;
goto done;
case -1:
sudo_warn("read");
goto bad;
goto done;
default:
msg_len -= nread;
rem -= nread;
cp += nread;
break;
}
} while (msg_len > 0);
} while (rem > 0);
}
msg = intercept_message__unpack(NULL, msg_len, buf);
if (msg == NULL) {
sudo_warnx("unable to unpack %s size %zu", "InterceptMessage",
(size_t)msg_len);
goto bad;
goto done;
}
if (msg->type_case != INTERCEPT_MESSAGE__TYPE_POLICY_CHECK_REQ) {
sudo_warnx(U_("unexpected type_case value %d in %s from %s"),
msg->type_case, "InterceptMessage", "sudo_intercept.so");
goto bad;
goto done;
}
closure->policy_result = intercept_check_policy(msg->u.policy_check_req,
@@ -693,17 +733,20 @@ intercept_read(int fd, struct intercept_closure *closure)
if (sudo_ev_set(&closure->ev, fd, SUDO_EV_WRITE, intercept_cb, closure) == -1) {
/* This cannot (currently) fail. */
sudo_warn("%s", U_("unable to add event to queue"));
goto bad;
goto done;
}
if (sudo_ev_add(base, &closure->ev, NULL, false) == -1) {
sudo_warn("%s", U_("unable to add event to queue"));
goto done;
}
goto done;
bad:
intercept_close(fd, closure);
ret = true;
done:
// XXX
//intercept_message__free_unpacked(msg, NULL);
free(buf);
debug_return;
debug_return_bool(ret);
}
static bool
@@ -796,72 +839,71 @@ fmt_error_message(struct intercept_closure *closure)
/*
* Write a response to sudo_intercept.so.
*/
static void
static bool
intercept_write(int fd, struct intercept_closure *closure)
{
size_t len = closure->len;
char *buf = closure->buf;
size_t rem;
uint8_t *cp;
ssize_t nwritten;
bool ret = false;
debug_decl(intercept_write, SUDO_DEBUG_EXEC);
switch (closure->policy_result) {
case 1:
if (!fmt_accept_message(closure))
goto bad;
goto done;
break;
case 0:
if (!fmt_reject_message(closure))
goto bad;
goto done;
break;
default:
if (!fmt_error_message(closure))
goto bad;
goto done;
break;
}
cp = closure->buf;
rem = closure->len;
do {
nwritten = write(fd, buf, len);
nwritten = write(fd, cp, rem);
if (nwritten == -1) {
sudo_warn("write");
goto bad;
goto done;
}
buf += nwritten;
len -= nwritten;
} while (len > 0);
cp += nwritten;
rem -= nwritten;
} while (rem > 0);
intercept_closure_reset(closure);
ret = true;
/* Switch event to read mode for the next request. */
if (sudo_ev_set(&closure->ev, fd, SUDO_EV_READ, intercept_cb, closure) == -1) {
/* This cannot (currently) fail. */
sudo_warn("%s", U_("unable to add event to queue"));
}
debug_return;
bad:
intercept_close(fd, closure);
debug_return;
done:
debug_return_bool(ret);
}
static void
intercept_cb(int fd, int what, void *v)
{
struct intercept_closure *closure = v;
bool success = false;
debug_decl(intercept_cb, SUDO_DEBUG_EXEC);
switch (what) {
case SUDO_EV_READ:
intercept_read(fd, closure);
success = intercept_read(fd, closure);
break;
case SUDO_EV_WRITE:
intercept_write(fd, closure);
success = intercept_write(fd, closure);
break;
default:
sudo_warnx("%s: unexpected event type %d", __func__, what);
break;
}
if (!success || what == SUDO_EV_WRITE) {
intercept_close(fd, closure);
}
debug_return;
}

48
src/exec_common.c
View File

@@ -23,6 +23,7 @@
#include <config.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@@ -40,10 +41,10 @@
* Add a DSO file to LD_PRELOAD or the system equivalent.
*/
static char **
preload_dso(char *envp[], const char *dso_file)
preload_dso(char *envp[], const char *dso_file, char * const extra_envp[])
{
char *preload = NULL;
int env_len;
int env_len, extra_len = 0;
int preload_idx = -1;
bool present = false;
# ifdef RTLD_PRELOAD_ENABLE_VAR
@@ -92,19 +93,28 @@ preload_dso(char *envp[], const char *dso_file)
}
# endif
}
if (extra_envp != NULL) {
for (extra_len = 0; extra_envp[extra_len] != NULL; extra_len++) {
continue;
}
}
/*
* Make a new copy of envp as needed.
* It would be nice to realloc the old envp[] but we don't know
* whether it was dynamically allocated. [TODO: plugin API]
*/
if (preload_idx == -1 || !enabled) {
const int env_size = env_len + 1 + (preload_idx == -1) + enabled; // -V547
if (preload_idx == -1 || !enabled || extra_len != 0) {
const int env_size = env_len + 1 + (preload_idx == -1) + enabled + extra_len; // -V547
char **nenvp = reallocarray(NULL, env_size, sizeof(*envp));
if (nenvp == NULL)
sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
memcpy(nenvp, envp, env_len * sizeof(*envp));
if (extra_envp != NULL) {
for (extra_len = 0; extra_envp[extra_len] != NULL; extra_len++)
nenvp[env_len++] = extra_envp[extra_len];
}
nenvp[env_len] = NULL;
envp = nenvp;
}
@@ -167,7 +177,7 @@ disable_execute(char *envp[], const char *dso)
#ifdef RTLD_PRELOAD_VAR
if (dso != NULL)
envp = preload_dso(envp, dso);
envp = preload_dso(envp, dso, NULL);
#endif /* RTLD_PRELOAD_VAR */
debug_return_ptr(envp);
@@ -178,15 +188,29 @@ disable_execute(char *envp[], const char *dso)
* Uses LD_PRELOAD and the like to perform a policy check on child commands.
*/
static char **
enable_intercept(char *envp[], const char *dso, int backchannel)
enable_intercept(char *envp[], const char *dso, int intercept_fd)
{
#ifdef RTLD_PRELOAD_VAR
char *env_add[] = { NULL, NULL };
debug_decl(enable_intercept, SUDO_DEBUG_UTIL);
#ifdef RTLD_PRELOAD_VAR
if (dso != NULL) {
/* XXX - add backchannel fd number to environment too (minimum 64) */
envp = preload_dso(envp, dso);
if (dso == NULL)
sudo_fatalx("%s: missing DSO", __func__);
if (intercept_fd == -1)
sudo_fatalx("%s: no intercept fd", __func__);
if (intercept_fd < INTERCEPT_FD_MIN) {
intercept_fd = fcntl(intercept_fd, F_DUPFD, INTERCEPT_FD_MIN);
if (intercept_fd == -1)
sudo_fatal("%s", U_("unable to dup intercept fd"));
}
if (asprintf(&env_add[0], "SUDO_INTERCEPT_FD=%d", intercept_fd) == -1)
debug_return_ptr(NULL);
envp = preload_dso(envp, dso, env_add);
#else
/* Intercept not supported, envp unchanged. */
if (intercept_fd != -1)
close(intercept_fd);
#endif /* RTLD_PRELOAD_VAR */
debug_return_ptr(envp);
@@ -198,7 +222,7 @@ enable_intercept(char *envp[], const char *dso, int backchannel)
*/
int
sudo_execve(int fd, const char *path, char *const argv[], char *envp[],
int backchannel, int flags)
int intercept_fd, int flags)
{
debug_decl(sudo_execve, SUDO_DEBUG_UTIL);
@@ -208,7 +232,7 @@ sudo_execve(int fd, const char *path, char *const argv[], char *envp[],
if (ISSET(flags, CD_NOEXEC))
envp = disable_execute(envp, sudo_conf_noexec_path());
else if (ISSET(flags, CD_INTERCEPT|CD_LOG_CHILDREN))
envp = enable_intercept(envp, sudo_conf_intercept_path(), backchannel);
envp = enable_intercept(envp, sudo_conf_intercept_path(), intercept_fd);
#ifdef HAVE_FEXECVE
if (fd != -1)

3
src/sudo_exec.h
View File

@@ -79,6 +79,9 @@
#define SESH_ERR_NO_FILES 32 /* copy error, no files copied */
#define SESH_ERR_SOME_FILES 33 /* copy error, some files copied */
#define INTERCEPT_FD_MIN 64 /* minimum fd so shell won't close it */
#define MESSAGE_SIZE_MAX 2097152 /* 2Mib max intercept message size */
/*
* Symbols shared between exec.c, exec_nopty.c, exec_pty.c and exec_monitor.c
*/

126
src/sudo_intercept.c Normal file
View File

@@ -0,0 +1,126 @@
/*
* SPDX-License-Identifier: ISC
*
* Copyright (c) 2021 Todd C. Miller <Todd.Miller@sudo.ws>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/*
* This is an open source non-commercial project. Dear PVS-Studio, please check it.
* PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
*/
#include <config.h>
#include <sys/types.h>
#include <errno.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#ifdef HAVE_STDBOOL_H
# include <stdbool.h>
#else
# include "compat/stdbool.h"
#endif /* HAVE_STDBOOL_H */
#if defined(HAVE_SHL_LOAD)
# include <dl.h>
#elif defined(HAVE_DLOPEN)
# include <dlfcn.h>
#endif
#include "sudo_compat.h"
#include "pathnames.h"
extern bool command_allowed(const char *cmnd, char * const argv[], char * const envp[], char **ncmnd, char ***nargv, char ***nenvp);
#ifdef HAVE___INTERPOSE
/*
* Mac OS X 10.4 and above has support for library symbol interposition.
* There is a good explanation of this in the Mac OS X Internals book.
*/
typedef struct interpose_s {
void *new_func;
void *orig_func;
} interpose_t;
static int
my_execve(const char *cmnd, char * const argv[], char * const envp[])
{
char *ncmnd = NULL, **nargv = NULL, **nenvp = NULL;
/* XXX - add SUDO_INTERCEPT_FD to environment as needed. */
if (command_allowed(cmnd, argv, envp, &ncmnd, &nargv, &nenvp)) {
/* Execute the command using the "real" execve() function. */
execve(ncmnd, nargv, nenvp);
} else {
errno = EACCES;
}
/* XXX - free ncmnd, nargv, nenvp */
return -1;
}
/* Magic to tell dyld to do symbol interposition. */
__attribute__((__used__)) static const interpose_t interposers[]
__attribute__((__section__("__DATA,__interpose"))) = {
{ (void *)my_execve, (void *)execve }
};
#else /* HAVE___INTERPOSE */
typedef int (*sudo_fn_execve_t)(const char *, char *const *, char *const *);
sudo_dso_public int
execve(const char *cmnd, char * const argv[], char * const envp[])
{
char *ncmnd = NULL, **nargv = NULL, **nenvp = NULL;
# if defined(HAVE_DLOPEN)
void *fn = dlsym(RTLD_NEXT, "execve");
# elif defined(HAVE_SHL_LOAD)
const char *name, *myname = _PATH_SUDO_INTERCEPT;
struct shl_descriptor *desc;
void *fn = NULL;
int idx = 0;
/* Search for execve() but skip this shared object. */
myname = sudo_basename(myname);
while (shl_get(idx++, &desc) == 0) {
name = sudo_basename(desc->filename);
if (strcmp(name, myname) == 0)
continue;
if (shl_findsym(&desc->handle, "execve", TYPE_PROCEDURE, &fn) == 0)
break;
}
# else
void *fn = NULL;
# endif
if (fn == NULL) {
errno = EACCES;
return -1;
}
/* XXX - add SUDO_INTERCEPT_FD to environment as needed. */
if (command_allowed(cmnd, argv, envp, &ncmnd, &nargv, &nenvp)) {
/* Execute the command using the "real" execve() function. */
return ((sudo_fn_execve_t)fn)(ncmnd, nargv, nenvp);
} else {
errno = EACCES;
}
/* XXX - free ncmnd, nargv, nenvp */
return -1;
}
#endif /* HAVE___INTERPOSE) */

313
src/sudo_intercept_common.c Normal file
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@@ -0,0 +1,313 @@
/*
* SPDX-License-Identifier: ISC
*
* Copyright (c) 2021 Todd C. Miller <Todd.Miller@sudo.ws>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/*
* This is an open source non-commercial project. Dear PVS-Studio, please check it.
* PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
*/
#include <config.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#ifdef HAVE_STDBOOL_H
# include <stdbool.h>
#else
# include "compat/stdbool.h"
#endif /* HAVE_STDBOOL_H */
#define SUDO_ERROR_WRAP 0
#include "sudo_compat.h"
#include "sudo_fatal.h"
#include "sudo_exec.h"
#include "sudo_gettext.h"
#include "intercept.pb-c.h"
extern char **environ;
static pid_t mainpid = -1;
static int intercept_sock = -1;
/*
* Look up SUDO_INTERCEPT_FD in the environment.
* This function is run when the shared library is loaded.
*/
__attribute__((constructor)) static void
sudo_interposer_init(void)
{
static bool initialized;
char **p;
if (!initialized) {
initialized = true;
mainpid = getpid();
/*
* Missing SUDO_INTERCEPT_FD will result in execve() failure.
* Note that we cannot use getenv(3) here on Linux at least.
*/
for (p = environ; *p != NULL; p++) {
if (strncmp(*p, "SUDO_INTERCEPT_FD=", sizeof("SUDO_INTERCEPT_FD=") -1) == 0) {
const char *fdstr = *p + sizeof("SUDO_INTERCEPT_FD=") - 1;
char *ep;
long ulval;
/* XXX - debugging */
ulval = strtoul(fdstr, &ep, 10);
if (*fdstr == '\0' || *ep != '\0' || ulval > INT_MAX) {
sudo_warnx(U_("invalid SUDO_INTERCEPT_FD: %s"), fdstr);
break;
}
intercept_sock = ulval;
break;
}
}
}
}
static uint8_t *
fmt_policy_check_req(const char *cmnd, char * const argv[], char * const envp[],
size_t *buflen)
{
InterceptMessage msg = INTERCEPT_MESSAGE__INIT;
PolicyCheckRequest req = POLICY_CHECK_REQUEST__INIT;
uint8_t *buf = NULL;
uint32_t msg_len;
size_t len;
/* Setup policy check request. */
req.command = (char *)cmnd;
req.argv = (char **)argv;
for (len = 0; argv[len] != NULL; len++)
continue;
req.n_argv = len;
req.envp = (char **)envp;
for (len = 0; envp[len] != NULL; len++)
continue;
req.n_envp = len;
msg.type_case = INTERCEPT_MESSAGE__TYPE_POLICY_CHECK_REQ;
msg.u.policy_check_req = &req;
len = intercept_message__get_packed_size(&msg);
if (len > MESSAGE_SIZE_MAX) {
sudo_warnx(U_("client message too large: %zu"), len);
goto done;
}
/* Wire message size is used for length encoding, precedes message. */
msg_len = len;
len += sizeof(msg_len);
if ((buf = malloc(len)) == NULL) {
sudo_warnx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
goto done;
}
memcpy(buf, &msg_len, sizeof(msg_len));
intercept_message__pack(&msg, buf + sizeof(msg_len));
*buflen = len;
done:
return buf;
}
/* Send fd over a unix domain socket. */
static bool
intercept_send_fd(int sock, int fd)
{
struct msghdr msg;
union {
struct cmsghdr hdr;
char buf[CMSG_SPACE(sizeof(int))];
} cmsgbuf;
struct cmsghdr *cmsg;
struct iovec iov[1];
char ch = '\0';
ssize_t nsent;
/*
* We send a single byte of data along with the fd; some systems
* don't support sending file descriptors without data.
* Note that the intercept fd is *blocking*.
*/
iov[0].iov_base = &ch;
iov[0].iov_len = 1;
memset(&msg, 0, sizeof(msg));
memset(&cmsgbuf, 0, sizeof(cmsgbuf));
msg.msg_iov = iov;
msg.msg_iovlen = 1;
msg.msg_control = &cmsgbuf.buf;
msg.msg_controllen = sizeof(cmsgbuf.buf);
cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_len = CMSG_LEN(sizeof(int));
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
*(int *)CMSG_DATA(cmsg) = fd;
for (;;) {
nsent = sendmsg(sock, &msg, 0);
if (nsent != -1)
return true;
if (errno != EAGAIN && errno != EINTR)
break;
}
sudo_warn("sendmsg");
return false;
}
bool
command_allowed(const char *cmnd, char * const argv[], char * const envp[],
char **ncmnd, char ***nargv, char ***nenvp)
{
PolicyCheckResult *res = NULL;
int sv[2] = { -1, -1 };
ssize_t nread, nwritten;
uint8_t *cp, *buf = NULL;
bool ret = false;
uint32_t res_len;
size_t len;
if (intercept_sock < INTERCEPT_FD_MIN) {
sudo_warnx("invalid intercept fd: %d", intercept_sock); // XXX debugging
errno = EINVAL;
goto done;
}
if (fcntl(intercept_sock, F_GETFD, 0) == -1) {
sudo_warnx("intercept fd %d not open", intercept_sock); // XXX debugging
errno = EINVAL;
goto done;
}
/* Don't allow the original process to be replaced. */
if (getpid() == mainpid) {
sudo_warnx("shell overwrite denied"); // XXX
// XXX debugging
errno = EACCES;
goto done;
}
/*
* We communicate with the main sudo process over a socket pair
* which is passed over the intercept_sock. The reason for not
* using intercept_sock directly is that multiple processes
* could be trying to use it at once. Sending an fd like this
* is atomic but regular communication is not.
*/
if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1) {
sudo_warn("socketpair");
goto done;
}
if (!intercept_send_fd(intercept_sock, sv[1]))
goto done;
close(sv[1]);
sv[1] = -1;
buf = fmt_policy_check_req(cmnd, argv, envp, &len);
if (buf == NULL)
goto done;
/* Send request to sudo (blocking). */
cp = buf;
do {
nwritten = write(sv[0], cp, len);
if (nwritten == -1) {
goto done;
}
len -= nwritten;
cp += nwritten;
} while (len > 0);
free(buf);
buf = NULL;
/* Read message size (uint32_t in host byte order). */
nread = read(sv[0], &res_len, sizeof(res_len));
if ((size_t)nread != sizeof(res_len)) {
if (nread == 0)
sudo_warnx("unexpected EOF reading message size"); // XXX
else
sudo_warn("read");
goto done;
}
if (res_len > MESSAGE_SIZE_MAX) {
sudo_warnx(U_("server message too large: %zu"), (size_t)res_len);
goto done;
}
/* Read response from sudo (blocking). */
if ((buf = malloc(res_len)) == NULL) {
goto done;
}
nread = read(sv[0], buf, res_len);
if ((size_t)nread != res_len) {
if (nread == 0)
sudo_warnx("unexpected EOF reading response"); // XXX
else
sudo_warn("read");
goto done;
}
res = policy_check_result__unpack(NULL, res_len, buf);
if (res == NULL) {
sudo_warnx("unable to unpack %s size %zu", "PolicyCheckResult",
(size_t)res_len);
goto done;
}
switch (res->type_case) {
case POLICY_CHECK_RESULT__TYPE_ACCEPT_MSG:
// XXX - return value
*ncmnd = strdup(res->u.accept_msg->run_command);
*nargv = reallocarray(NULL, res->u.accept_msg->n_run_argv + 1, sizeof(char *));
for (len = 0; len < res->u.accept_msg->n_run_argv; len++) {
(*nargv)[len] = strdup(res->u.accept_msg->run_argv[len]);
}
(*nargv)[len] = NULL;
/* XXX - add SUDO_INTERCEPT_FD to environment as needed. */
*nenvp = (char **)envp;
ret = true;
break;
case POLICY_CHECK_RESULT__TYPE_REJECT_MSG:
/* XXX - display reject message */
break;
case POLICY_CHECK_RESULT__TYPE_ERROR_MSG:
/* XXX - display error message */
break;
default:
sudo_warnx(U_("unexpected type_case value %d in %s from %s"),
res->type_case, "PolicyCheckResult", "sudo");
break;
}
done:
policy_check_result__free_unpacked(res, NULL);
if (sv[0] != -1)
close(sv[0]);
if (sv[1] != -1)
close(sv[1]);
free(buf);
return ret;
}