This is a note to let you know that I've just added the patch titled
userns: Don't allow CLONE_NEWUSER | CLONE_FS
to the 3.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
userns-don-t-allow-clone_newuser-clone_fs.patch
and it can be found in the queue-3.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From e66eded8309ebf679d3d3c1f5820d1f2ca332c71 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Date: Wed, 13 Mar 2013 11:51:49 -0700
Subject: userns: Don't allow CLONE_NEWUSER | CLONE_FS
From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
commit e66eded8309ebf679d3d3c1f5820d1f2ca332c71 upstream.
Don't allowing sharing the root directory with processes in a
different user namespace. There doesn't seem to be any point, and to
allow it would require the overhead of putting a user namespace
reference in fs_struct (for permission checks) and incrementing that
reference count on practically every call to fork.
So just perform the inexpensive test of forbidding sharing fs_struct
acrosss processes in different user namespaces. We already disallow
other forms of threading when unsharing a user namespace so this
should be no real burden in practice.
This updates setns, clone, and unshare to disallow multiple user
namespaces sharing an fs_struct.
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/fork.c | 5 ++++-
kernel/user_namespace.c | 4 ++++
2 files changed, 8 insertions(+), 1 deletion(-)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1141,6 +1141,9 @@ static struct task_struct *copy_process(
if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
return ERR_PTR(-EINVAL);
+ if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
+ return ERR_PTR(-EINVAL);
+
/*
* Thread groups must share signals as well, and detached threads
* can only be started up within the thread group.
@@ -1801,7 +1804,7 @@ SYSCALL_DEFINE1(unshare, unsigned long,
* If unsharing a user namespace must also unshare the thread.
*/
if (unshare_flags & CLONE_NEWUSER)
- unshare_flags |= CLONE_THREAD;
+ unshare_flags |= CLONE_THREAD | CLONE_FS;
/*
* If unsharing a pid namespace must also unshare the thread.
*/
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -21,6 +21,7 @@
#include <linux/uaccess.h>
#include <linux/ctype.h>
#include <linux/projid.h>
+#include <linux/fs_struct.h>
static struct kmem_cache *user_ns_cachep __read_mostly;
@@ -803,6 +804,9 @@ static int userns_install(struct nsproxy
if (atomic_read(¤t->mm->mm_users) > 1)
return -EINVAL;
+ if (current->fs->users != 1)
+ return -EINVAL;
+
if (!ns_capable(user_ns, CAP_SYS_ADMIN))
return -EPERM;
Patches currently in stable-queue which might be from ebiederm@xxxxxxxxxxxx are
queue-3.8/userns-stop-oopsing-in-key_change_session_keyring.patch
queue-3.8/userns-don-t-allow-clone_newuser-clone_fs.patch
queue-3.8/proc-use-nd_jump_link-in-proc_ns_follow_link.patch
--
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