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support_enter_mount_namespace: Unshare with mount --make-rprivate

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System defaults vary, and a mere unshare (CLONE_NEWNS) (which is part of
support_become_root) is no longer sufficient.

Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
This commit is contained in:
Florian Weimer 2017-11-18 14:30:20 +01:00
parent 8adfb0eeff
commit 273a0c4983
4 changed files with 58 additions and 0 deletions
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7
ChangeLog
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@ -1,3 +1,10 @@
2017-11-18 Florian Weimer <fweimer@redhat.com>
* support/namespace.h (support_enter_mount_namespace): Declare.
* support/support_enter_mount_namespace.c: New file.
* support/Makefile (libsupport-routines): Add
support_enter_mount_namespace.
2017-11-18 Florian Weimer <fweimer@redhat.com>
* support/temp_file.c (support_create_temp_directory): Use

1
support/Makefile
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@ -42,6 +42,7 @@ libsupport-routines = \
support_capture_subprocess \
support_capture_subprocess_check \
support_chroot \
support_enter_mount_namespace \
support_enter_network_namespace \
support_format_address_family \
support_format_addrinfo \

5
support/namespace.h
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@ -51,6 +51,11 @@ bool support_can_chroot (void);
has sufficient privileges. */
bool support_enter_network_namespace (void);
/* Enter a mount namespace and mark / as private (not shared). If
this function returns true, mount operations in this process will
not affect the host system afterwards. */
bool support_enter_mount_namespace (void);
/* Return true if support_enter_network_namespace managed to enter a
UTS namespace. */
bool support_in_uts_namespace (void);

45
support/support_enter_mount_namespace.c Normal file
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@ -0,0 +1,45 @@
/* Enter a mount namespace.
Copyright (C) 2017 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
<http://www.gnu.org/licenses/>. */
#include <support/namespace.h>
#include <sched.h>
#include <stdio.h>
#include <sys/mount.h>
bool
support_enter_mount_namespace (void)
{
#ifdef CLONE_NEWNS
if (unshare (CLONE_NEWNS) == 0)
{
/* On some systems, / is marked as MS_SHARED, which means that
mounts within the namespace leak to the rest of the system,
which is not what we want. */
if (mount ("none", "/", NULL, MS_REC | MS_PRIVATE, NULL) != 0)
{
printf ("warning: making the mount namespace private failed: %m\n");
return false;
}
return true;
}
else
printf ("warning: unshare (CLONE_NEWNS) failed: %m\n");
#endif /* CLONE_NEWNS */
return false;
}