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103 lines
3.2 KiB
C
103 lines
3.2 KiB
C
/* Acquire root privileges.
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Copyright (C) 2016-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <support/namespace.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <sched.h>
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#include <stdio.h>
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#include <string.h>
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#include <support/check.h>
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#include <support/xunistd.h>
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#include <unistd.h>
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#ifdef CLONE_NEWUSER
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/* The necessary steps to allow file creation in user namespaces. */
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static void
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setup_uid_gid_mapping (uid_t original_uid, gid_t original_gid)
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{
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int fd = open64 ("/proc/self/uid_map", O_WRONLY);
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if (fd < 0)
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{
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printf ("warning: could not open /proc/self/uid_map: %m\n"
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"warning: file creation may not be possible\n");
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return;
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}
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/* We map our original UID to the same UID in the container so we
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own our own files normally. Without that, file creation could
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fail with EOVERFLOW (sic!). */
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char buf[100];
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int ret = snprintf (buf, sizeof (buf), "%llu %llu 1\n",
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(unsigned long long) original_uid,
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(unsigned long long) original_uid);
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TEST_VERIFY_EXIT (ret < sizeof (buf));
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xwrite (fd, buf, ret);
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xclose (fd);
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/* Linux 3.19 introduced the setgroups file. We need write "deny" to this
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file otherwise writing to gid_map will fail with EPERM. */
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fd = open64 ("/proc/self/setgroups", O_WRONLY, 0);
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if (fd < 0)
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{
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if (errno != ENOENT)
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FAIL_EXIT1 ("open64 (\"/proc/self/setgroups\", 0x%x, 0%o): %m",
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O_WRONLY, 0);
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/* This kernel doesn't expose the setgroups file so simply move on. */
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}
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else
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{
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xwrite (fd, "deny\n", strlen ("deny\n"));
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xclose (fd);
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}
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/* Now map our own GID, like we did for the user ID. */
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fd = xopen ("/proc/self/gid_map", O_WRONLY, 0);
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ret = snprintf (buf, sizeof (buf), "%llu %llu 1\n",
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(unsigned long long) original_gid,
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(unsigned long long) original_gid);
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TEST_VERIFY_EXIT (ret < sizeof (buf));
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xwrite (fd, buf, ret);
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xclose (fd);
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}
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#endif /* CLONE_NEWUSER */
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bool
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support_become_root (void)
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{
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#ifdef CLONE_NEWUSER
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uid_t original_uid = getuid ();
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gid_t original_gid = getgid ();
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if (unshare (CLONE_NEWUSER | CLONE_NEWNS) == 0)
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{
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setup_uid_gid_mapping (original_uid, original_gid);
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/* Even if we do not have UID zero, we have extended privileges at
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this point. */
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return true;
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}
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#endif
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if (setuid (0) != 0)
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{
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printf ("warning: could not become root outside namespace (%m)\n");
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return false;
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}
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return true;
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}
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