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authorEric W. Biederman <ebiederm@xmission.com>2013-03-13 11:51:49 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-03-14 11:26:37 -0700
commit364709ddeaaec519bc9014b05474aa071f3afc6f (patch)
parentf7322a37359d76075db32f826ce5c2c473391a5a (diff)
userns: Don't allow CLONE_NEWUSER | CLONE_FS
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@xmission.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2 files changed, 8 insertions, 1 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index c535f33bbb9c..5630e520671c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1141,6 +1141,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
return ERR_PTR(-EINVAL);
+ 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, unshare_flags)
* 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.
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 2b042c42fbc4..dbfe36a724f4 100644
--- 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 *nsproxy, void *ns)
if (atomic_read(&current->mm->mm_users) > 1)
return -EINVAL;
+ if (current->fs->users != 1)
+ return -EINVAL;
if (!ns_capable(user_ns, CAP_SYS_ADMIN))
return -EPERM;