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support: Add capability to fork an sgid child

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Add a new function support_capture_subprogram_self_sgid that spawns an
sgid child of the running program with its own image and returns the
exit code of the child process.  This functionality is used by at
least three tests in the testsuite at the moment, so it makes sense to
consolidate.

There is also a new function support_subprogram_wait which should
provide simple system() like functionality that does not set up file
actions.  This is useful in cases where only the return code of the
spawned subprocess is interesting.

This patch also ports tst-secure-getenv to this new function.  A
subsequent patch will port other tests.  This also brings an important
change to tst-secure-getenv behaviour.  Now instead of succeeding, the
test fails as UNSUPPORTED if it is unable to spawn a setgid child,
which is how it should have been in the first place.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

(cherry picked from commit 716a3bdc41)
This commit is contained in:
Siddhesh Poyarekar 2021-04-09 20:55:45 +05:30
parent 7fa6d30eea
commit 700264179c
5 changed files with 168 additions and 181 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

199
stdlib/tst-secure-getenv.c
View File

@ -30,167 +30,12 @@
#include <sys/wait.h>
#include <unistd.h>
#include <support/check.h>
#include <support/support.h>
#include <support/capture_subprocess.h>
#include <support/test-driver.h>
static char MAGIC_ARGUMENT[] = "run-actual-test";
#define MAGIC_STATUS 19
/* Return a GID which is not our current GID, but is present in the
supplementary group list. */
static gid_t
choose_gid (void)
{
int count = getgroups (0, NULL);
if (count < 0)
{
printf ("getgroups: %m\n");
exit (1);
}
gid_t *groups;
groups = xcalloc (count, sizeof (*groups));
int ret = getgroups (count, groups);
if (ret < 0)
{
printf ("getgroups: %m\n");
exit (1);
}
gid_t current = getgid ();
gid_t not_current = 0;
for (int i = 0; i < ret; ++i)
{
if (groups[i] != current)
{
not_current = groups[i];
break;
}
}
free (groups);
return not_current;
}
/* Copies the executable into a restricted directory, so that we can
safely make it SGID with the TARGET group ID. Then runs the
executable. */
static int
run_executable_sgid (gid_t target)
{
char *dirname = xasprintf ("%s/secure-getenv.%jd",
test_dir, (intmax_t) getpid ());
char *execname = xasprintf ("%s/bin", dirname);
int infd = -1;
int outfd = -1;
int ret = -1;
if (mkdir (dirname, 0700) < 0)
{
printf ("mkdir: %m\n");
goto err;
}
infd = open ("/proc/self/exe", O_RDONLY);
if (infd < 0)
{
printf ("open (/proc/self/exe): %m\n");
goto err;
}
outfd = open (execname, O_WRONLY | O_CREAT | O_EXCL, 0700);
if (outfd < 0)
{
printf ("open (%s): %m\n", execname);
goto err;
}
char buf[4096];
for (;;)
{
ssize_t rdcount = read (infd, buf, sizeof (buf));
if (rdcount < 0)
{
printf ("read: %m\n");
goto err;
}
if (rdcount == 0)
break;
char *p = buf;
char *end = buf + rdcount;
while (p != end)
{
ssize_t wrcount = write (outfd, buf, end - p);
if (wrcount == 0)
errno = ENOSPC;
if (wrcount <= 0)
{
printf ("write: %m\n");
goto err;
}
p += wrcount;
}
}
if (fchown (outfd, getuid (), target) < 0)
{
printf ("fchown (%s): %m\n", execname);
goto err;
}
if (fchmod (outfd, 02750) < 0)
{
printf ("fchmod (%s): %m\n", execname);
goto err;
}
if (close (outfd) < 0)
{
printf ("close (outfd): %m\n");
goto err;
}
if (close (infd) < 0)
{
printf ("close (infd): %m\n");
goto err;
}
int kid = fork ();
if (kid < 0)
{
printf ("fork: %m\n");
goto err;
}
if (kid == 0)
{
/* Child process. */
char *args[] = { execname, MAGIC_ARGUMENT, NULL };
execve (execname, args, environ);
printf ("execve (%s): %m\n", execname);
_exit (1);
}
int status;
if (waitpid (kid, &status, 0) < 0)
{
printf ("waitpid: %m\n");
goto err;
}
if (!WIFEXITED (status) || WEXITSTATUS (status) != MAGIC_STATUS)
{
printf ("Unexpected exit status %d from child process\n",
status);
goto err;
}
ret = 0;
err:
if (outfd >= 0)
close (outfd);
if (infd >= 0)
close (infd);
if (execname)
{
unlink (execname);
free (execname);
}
if (dirname)
{
rmdir (dirname);
free (dirname);
}
return ret;
}
static int
do_test (void)
@ -212,15 +57,15 @@ do_test (void)
exit (1);
}
gid_t target = choose_gid ();
if (target == 0)
{
fprintf (stderr,
"Could not find a suitable GID for user %jd, skipping test\n",
(intmax_t) getuid ());
exit (0);
}
return run_executable_sgid (target);
int status = support_capture_subprogram_self_sgid (MAGIC_ARGUMENT);
if (WEXITSTATUS (status) == EXIT_UNSUPPORTED)
return EXIT_UNSUPPORTED;
if (!WIFEXITED (status))
FAIL_EXIT1 ("Unexpected exit status %d from child process\n", status);
return 0;
}
static void
@ -229,23 +74,15 @@ alternative_main (int argc, char **argv)
if (argc == 2 && strcmp (argv[1], MAGIC_ARGUMENT) == 0)
{
if (getgid () == getegid ())
{
/* This can happen if the file system is mounted nosuid. */
fprintf (stderr, "SGID failed: GID and EGID match (%jd)\n",
(intmax_t) getgid ());
exit (MAGIC_STATUS);
}
/* This can happen if the file system is mounted nosuid. */
FAIL_UNSUPPORTED ("SGID failed: GID and EGID match (%jd)\n",
(intmax_t) getgid ());
if (getenv ("PATH") == NULL)
{
printf ("PATH variable not present\n");
exit (3);
}
FAIL_EXIT (3, "PATH variable not present\n");
if (secure_getenv ("PATH") != NULL)
{
printf ("PATH variable not filtered out\n");
exit (4);
}
exit (MAGIC_STATUS);
FAIL_EXIT (4, "PATH variable not filtered out\n");
exit (EXIT_SUCCESS);
}
}

6
support/capture_subprocess.h
View File

@ -41,6 +41,12 @@ struct support_capture_subprocess support_capture_subprocess
struct support_capture_subprocess support_capture_subprogram
(const char *file, char *const argv[]);
/* Copy the running program into a setgid binary and run it with CHILD_ID
argument. If execution is successful, return the exit status of the child
program, otherwise return a non-zero failure exit code. */
int support_capture_subprogram_self_sgid
(char *child_id);
/* Deallocate the subprocess data captured by
support_capture_subprocess. */
void support_capture_subprocess_free (struct support_capture_subprocess *);

5
support/subprocess.h
View File

@ -38,6 +38,11 @@ struct support_subprocess support_subprocess
struct support_subprocess support_subprogram
(const char *file, char *const argv[]);
/* Invoke program FILE with ARGV arguments by using posix_spawn and wait for it
to complete. Return program exit status. */
int support_subprogram_wait
(const char *file, char *const argv[]);
/* Wait for the subprocess indicated by PROC::PID. Return the status
indicate by waitpid call. */
int support_process_wait (struct support_subprocess *proc);

126
support/support_capture_subprocess.c
View File

@ -20,11 +20,14 @@
#include <support/capture_subprocess.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <support/check.h>
#include <support/xunistd.h>
#include <support/xsocket.h>
#include <support/xspawn.h>
#include <support/support.h>
#include <support/test-driver.h>
static void
transfer (const char *what, struct pollfd *pfd, struct xmemstream *stream)
@ -102,6 +105,129 @@ support_capture_subprogram (const char *file, char *const argv[])
return result;
}
/* Copies the executable into a restricted directory, so that we can
safely make it SGID with the TARGET group ID. Then runs the
executable. */
static int
copy_and_spawn_sgid (char *child_id, gid_t gid)
{
char *dirname = xasprintf ("%s/tst-tunables-setuid.%jd",
test_dir, (intmax_t) getpid ());
char *execname = xasprintf ("%s/bin", dirname);
int infd = -1;
int outfd = -1;
int ret = 1, status = 1;
TEST_VERIFY (mkdir (dirname, 0700) == 0);
if (support_record_failure_is_failed ())
goto err;
infd = open ("/proc/self/exe", O_RDONLY);
if (infd < 0)
FAIL_UNSUPPORTED ("unsupported: Cannot read binary from procfs\n");
outfd = open (execname, O_WRONLY | O_CREAT | O_EXCL, 0700);
TEST_VERIFY (outfd >= 0);
if (support_record_failure_is_failed ())
goto err;
char buf[4096];
for (;;)
{
ssize_t rdcount = read (infd, buf, sizeof (buf));
TEST_VERIFY (rdcount >= 0);
if (support_record_failure_is_failed ())
goto err;
if (rdcount == 0)
break;
char *p = buf;
char *end = buf + rdcount;
while (p != end)
{
ssize_t wrcount = write (outfd, buf, end - p);
if (wrcount == 0)
errno = ENOSPC;
TEST_VERIFY (wrcount > 0);
if (support_record_failure_is_failed ())
goto err;
p += wrcount;
}
}
TEST_VERIFY (fchown (outfd, getuid (), gid) == 0);
if (support_record_failure_is_failed ())
goto err;
TEST_VERIFY (fchmod (outfd, 02750) == 0);
if (support_record_failure_is_failed ())
goto err;
TEST_VERIFY (close (outfd) == 0);
if (support_record_failure_is_failed ())
goto err;
TEST_VERIFY (close (infd) == 0);
if (support_record_failure_is_failed ())
goto err;
/* We have the binary, now spawn the subprocess. Avoid using
support_subprogram because we only want the program exit status, not the
contents. */
ret = 0;
char * const args[] = {execname, child_id, NULL};
status = support_subprogram_wait (args[0], args);
err:
if (outfd >= 0)
close (outfd);
if (infd >= 0)
close (infd);
if (execname != NULL)
{
unlink (execname);
free (execname);
}
if (dirname != NULL)
{
rmdir (dirname);
free (dirname);
}
if (ret != 0)
FAIL_EXIT1("Failed to make sgid executable for test\n");
return status;
}
int
support_capture_subprogram_self_sgid (char *child_id)
{
gid_t target = 0;
const int count = 64;
gid_t groups[count];
/* Get a GID which is not our current GID, but is present in the
supplementary group list. */
int ret = getgroups (count, groups);
if (ret < 0)
FAIL_UNSUPPORTED("Could not get group list for user %jd\n",
(intmax_t) getuid ());
gid_t current = getgid ();
for (int i = 0; i < ret; ++i)
{
if (groups[i] != current)
{
target = groups[i];
break;
}
}
if (target == 0)
FAIL_UNSUPPORTED("Could not find a suitable GID for user %jd\n",
(intmax_t) getuid ());
return copy_and_spawn_sgid (child_id, target);
}
void
support_capture_subprocess_free (struct support_capture_subprocess *p)
{

13
support/support_subprocess.c
View File

@ -92,6 +92,19 @@ support_subprogram (const char *file, char *const argv[])
return result;
}
int
support_subprogram_wait (const char *file, char *const argv[])
{
posix_spawn_file_actions_t fa;
posix_spawn_file_actions_init (&fa);
struct support_subprocess res = support_subprocess_init ();
res.pid = xposix_spawn (file, &fa, NULL, argv, environ);
return support_process_wait (&res);
}
int
support_process_wait (struct support_subprocess *proc)
{