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contrib/capsicum-test/fexecve.cc

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#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sstream>
#include "syscalls.h"
#include "capsicum.h"
#include "capsicum-test.h"
// Arguments to use in execve() calls.
static char* null_envp[] = {NULL};
class Execve : public ::testing::Test {
public:
Execve() : exec_fd_(-1) {
// We need a program to exec(), but for fexecve() to work in capability
// mode that program needs to be statically linked (otherwise ld.so will
// attempt to traverse the filesystem to load (e.g.) /lib/libc.so and
// fail).
exec_prog_ = capsicum_test_bindir + "/mini-me";
exec_prog_noexec_ = capsicum_test_bindir + "/mini-me.noexec";
exec_prog_setuid_ = capsicum_test_bindir + "/mini-me.setuid";
exec_fd_ = open(exec_prog_.c_str(), O_RDONLY);
if (exec_fd_ < 0) {
fprintf(stderr, "Error! Failed to open %s\n", exec_prog_.c_str());
}
argv_checkroot_[0] = (char*)exec_prog_.c_str();
argv_fail_[0] = (char*)exec_prog_.c_str();
argv_pass_[0] = (char*)exec_prog_.c_str();
}
~Execve() {
if (exec_fd_ >= 0) {
close(exec_fd_);
exec_fd_ = -1;
}
}
protected:
char* argv_checkroot_[3] = {nullptr, (char*)"--checkroot", nullptr};
char* argv_fail_[3] = {nullptr, (char*)"--fail", nullptr};
char* argv_pass_[3] = {nullptr, (char*)"--pass", nullptr};
std::string exec_prog_, exec_prog_noexec_, exec_prog_setuid_;
int exec_fd_;
};
class Fexecve : public Execve {
public:
Fexecve() : Execve() {}
};
class FexecveWithScript : public Fexecve {
public:
FexecveWithScript() :
Fexecve(), temp_script_filename_(TmpFile("cap_sh_script")) {}
void SetUp() override {
// First, build an executable shell script
int fd = open(temp_script_filename_, O_RDWR|O_CREAT, 0755);
EXPECT_OK(fd);
const char* contents = "#!/bin/sh\nexit 99\n";
EXPECT_OK(write(fd, contents, strlen(contents)));
close(fd);
}
void TearDown() override {
(void)::unlink(temp_script_filename_);
}
const char *temp_script_filename_;
};
FORK_TEST_F(Execve, BasicFexecve) {
EXPECT_OK(fexecve_(exec_fd_, argv_pass_, null_envp));
// Should not reach here, exec() takes over.
EXPECT_TRUE(!"fexecve() should never return");
}
FORK_TEST_F(Execve, InCapMode) {
EXPECT_OK(cap_enter());
EXPECT_OK(fexecve_(exec_fd_, argv_pass_, null_envp));
// Should not reach here, exec() takes over.
EXPECT_TRUE(!"fexecve() should never return");
}
FORK_TEST_F(Execve, FailWithoutCap) {
EXPECT_OK(cap_enter());
int cap_fd = dup(exec_fd_);
EXPECT_OK(cap_fd);
cap_rights_t rights;
cap_rights_init(&rights, 0);
EXPECT_OK(cap_rights_limit(cap_fd, &rights));
EXPECT_EQ(-1, fexecve_(cap_fd, argv_fail_, null_envp));
EXPECT_EQ(ENOTCAPABLE, errno);
}
FORK_TEST_F(Execve, SucceedWithCap) {
EXPECT_OK(cap_enter());
int cap_fd = dup(exec_fd_);
EXPECT_OK(cap_fd);
cap_rights_t rights;
// TODO(drysdale): would prefer that Linux Capsicum not need all of these
// rights -- just CAP_FEXECVE|CAP_READ or CAP_FEXECVE would be preferable.
cap_rights_init(&rights, CAP_FEXECVE, CAP_LOOKUP, CAP_READ);
EXPECT_OK(cap_rights_limit(cap_fd, &rights));
EXPECT_OK(fexecve_(cap_fd, argv_pass_, null_envp));
// Should not reach here, exec() takes over.
EXPECT_TRUE(!"fexecve() should have succeeded");
}
FORK_TEST_F(Fexecve, ExecutePermissionCheck) {
int fd = open(exec_prog_noexec_.c_str(), O_RDONLY);
EXPECT_OK(fd);
if (fd >= 0) {
struct stat data;
EXPECT_OK(fstat(fd, &data));
EXPECT_EQ((mode_t)0, data.st_mode & (S_IXUSR|S_IXGRP|S_IXOTH));
EXPECT_EQ(-1, fexecve_(fd, argv_fail_, null_envp));
EXPECT_EQ(EACCES, errno);
close(fd);
}
}
FORK_TEST_F(Fexecve, SetuidIgnored) {
if (geteuid() == 0) {
TEST_SKIPPED("requires non-root");
return;
}
int fd = open(exec_prog_setuid_.c_str(), O_RDONLY);
EXPECT_OK(fd);
EXPECT_OK(cap_enter());
if (fd >= 0) {
struct stat data;
EXPECT_OK(fstat(fd, &data));
EXPECT_EQ((mode_t)S_ISUID, data.st_mode & S_ISUID);
EXPECT_OK(fexecve_(fd, argv_checkroot_, null_envp));
// Should not reach here, exec() takes over.
EXPECT_TRUE(!"fexecve() should have succeeded");
close(fd);
}
}
FORK_TEST_F(Fexecve, ExecveFailure) {
EXPECT_OK(cap_enter());
EXPECT_EQ(-1, execve(argv_fail_[0], argv_fail_, null_envp));
EXPECT_EQ(ECAPMODE, errno);
}
FORK_TEST_F(FexecveWithScript, CapModeScriptFail) {
int fd;
// Open the script file, with CAP_FEXECVE rights.
fd = open(temp_script_filename_, O_RDONLY);
cap_rights_t rights;
cap_rights_init(&rights, CAP_FEXECVE, CAP_READ, CAP_SEEK);
EXPECT_OK(cap_rights_limit(fd, &rights));
EXPECT_OK(cap_enter()); // Enter capability mode
// Attempt fexecve; should fail, because "/bin/sh" is inaccessible.
EXPECT_EQ(-1, fexecve_(fd, argv_pass_, null_envp));
}
#ifdef HAVE_EXECVEAT
TEST(Execveat, NoUpwardTraversal) {
char *abspath = realpath(exec_prog_, NULL);
char cwd[1024];
getcwd(cwd, sizeof(cwd));
int dfd = open(".", O_DIRECTORY|O_RDONLY);
pid_t child = fork();
if (child == 0) {
EXPECT_OK(cap_enter()); // Enter capability mode.
// Can't execveat() an absolute path, even relative to a dfd.
EXPECT_SYSCALL_FAIL(ECAPMODE,
execveat(AT_FDCWD, abspath, argv_pass_, null_envp, 0));
EXPECT_SYSCALL_FAIL(E_NO_TRAVERSE_CAPABILITY,
execveat(dfd, abspath, argv_pass_, null_envp, 0));
// Can't execveat() a relative path ("../<dir>/./<exe>").
char *p = cwd + strlen(cwd);
while (*p != '/') p--;
char buffer[1024] = "../";
strcat(buffer, ++p);
strcat(buffer, "/");
strcat(buffer, exec_prog_);
EXPECT_SYSCALL_FAIL(E_NO_TRAVERSE_CAPABILITY,
execveat(dfd, buffer, argv_pass_, null_envp, 0));
exit(HasFailure() ? 99 : 123);
}
int status;
EXPECT_EQ(child, waitpid(child, &status, 0));
EXPECT_TRUE(WIFEXITED(status)) << "0x" << std::hex << status;
EXPECT_EQ(123, WEXITSTATUS(status));
free(abspath);
close(dfd);
}
#endif