userns: Don't allow CLONE_NEWUSER | CLONE_FS (e66eded8) · Commits · 戴 / test

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. Cc: stable@vger.kernel.org Signed-off-by:

"Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

kernel/fork.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -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);

		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.
		@@ -1807,7 +1810,7 @@ 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.
		*/

kernel/user_namespace.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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;

		@@ -837,6 +838,9 @@ 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;

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