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/* Acquire root privileges.
Copyright (C) 2016-2023 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <support/namespace.h>
#include <errno.h>
#include <fcntl.h>
#include <sched.h>
#include <stdio.h>
#include <string.h>
#include <support/check.h>
#include <support/xunistd.h>
#include <unistd.h>
#ifdef CLONE_NEWUSER
/* The necessary steps to allow file creation in user namespaces. */
static void
setup_uid_gid_mapping (uid_t original_uid, gid_t original_gid)
{
int fd = open64 ("/proc/self/uid_map", O_WRONLY);
if (fd < 0)
{
printf ("warning: could not open /proc/self/uid_map: %m\n"
"warning: file creation may not be possible\n");
return;
}
/* We map our original UID to the same UID in the container so we
own our own files normally. Without that, file creation could
fail with EOVERFLOW (sic!). */
char buf[100];
int ret = snprintf (buf, sizeof (buf), "%llu %llu 1\n",
(unsigned long long) original_uid,
(unsigned long long) original_uid);
TEST_VERIFY_EXIT (ret < sizeof (buf));
xwrite (fd, buf, ret);
xclose (fd);
/* Linux 3.19 introduced the setgroups file. We need write "deny" to this
file otherwise writing to gid_map will fail with EPERM. */
fd = open64 ("/proc/self/setgroups", O_WRONLY, 0);
if (fd < 0)
{
if (errno != ENOENT)
FAIL_EXIT1 ("open64 (\"/proc/self/setgroups\", 0x%x, 0%o): %m",
O_WRONLY, 0);
/* This kernel doesn't expose the setgroups file so simply move on. */
}
else
{
xwrite (fd, "deny\n", strlen ("deny\n"));
xclose (fd);
}
/* Now map our own GID, like we did for the user ID. */
fd = xopen ("/proc/self/gid_map", O_WRONLY, 0);
ret = snprintf (buf, sizeof (buf), "%llu %llu 1\n",
(unsigned long long) original_gid,
(unsigned long long) original_gid);
TEST_VERIFY_EXIT (ret < sizeof (buf));
xwrite (fd, buf, ret);
xclose (fd);
}
#endif /* CLONE_NEWUSER */
bool
support_become_root (void)
{
#ifdef CLONE_NEWUSER
uid_t original_uid = getuid ();
gid_t original_gid = getgid ();
if (unshare (CLONE_NEWUSER | CLONE_NEWNS) == 0)
{
setup_uid_gid_mapping (original_uid, original_gid);
/* Even if we do not have UID zero, we have extended privileges at
this point. */
return true;
}
#endif
if (setuid (0) != 0)
{
printf ("warning: could not become root outside namespace (%m)\n");
return false;
}
return true;
}
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