Unverified Commit 42815808 authored Jul 06, 2020 by Christian Brauner

timens: make vdso_join_timens() always succeed

As discussed on-list (cf. [1]), in order to make setns() support time
namespaces when attaching to multiple namespaces at once properly we
need to tweak vdso_join_timens() to always succeed. So switch
vdso_join_timens() to using a read lock and replacing
mmap_write_lock_killable() to mmap_read_lock() as we discussed.

Last cycle setns() was changed to support attaching to multiple namespaces
atomically. This requires all namespaces to have a point of no return where
they can't fail anymore. Specifically, <namespace-type>_install() is
allowed to perform permission checks and install the namespace into the new
struct nsset that it has been given but it is not allowed to make visible
changes to the affected task. Once <namespace-type>_install() returns
anything that the given namespace type requires to be setup in addition
needs to ideally be done in a function that can't fail or if it fails the
failure is not fatal. For time namespaces the relevant functions that fall
into this category are timens_set_vvar_page() and vdso_join_timens().
Currently the latter can fail but doesn't need to. With this we can go on
to implement a timens_commit() helper in a follow up patch to be used by
setns().

[1]: https://lore.kernel.org/lkml/20200611110221.pgd3r5qkjrjmfqa2@wittgenstein



Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Andrei Vagin <avagin@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Dmitry Safonov <dima@arista.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20200706154912.3248030-2-christian.brauner@ubuntu.com

parent dcb7fd82

arch/x86/entry/vdso/vma.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -144,8 +144,7 @@ int vdso_join_timens(struct task_struct task, struct time_namespace ns)
		struct mm_struct *mm = task->mm;
		struct vm_area_struct *vma;

		if (mmap_write_lock_killable(mm))
		return -EINTR;
		mmap_read_lock(mm);

		for (vma = mm->mmap; vma; vma = vma->vm_next) {
		unsigned long size = vma->vm_end - vma->vm_start;
		@@ -154,7 +153,7 @@ int vdso_join_timens(struct task_struct task, struct time_namespace ns)
		zap_page_range(vma, vma->vm_start, size);
		}

		mmap_write_unlock(mm);
		mmap_read_unlock(mm);
		return 0;
		}
		#else

kernel/time/namespace.c

+2 −8

Original line number	Diff line number	Diff line
		@@ -284,7 +284,6 @@ static int timens_install(struct nsset nsset, struct ns_common new)
		{
		struct nsproxy *nsproxy = nsset->nsproxy;
		struct time_namespace *ns = to_time_ns(new);
		int err;

		if (!current_is_single_threaded())
		return -EUSERS;
		@@ -295,9 +294,7 @@ static int timens_install(struct nsset nsset, struct ns_common new)

		timens_set_vvar_page(current, ns);

		err = vdso_join_timens(current, ns);
		if (err)
		return err;
		vdso_join_timens(current, ns);

		get_time_ns(ns);
		put_time_ns(nsproxy->time_ns);
		@@ -313,7 +310,6 @@ int timens_on_fork(struct nsproxy nsproxy, struct task_struct tsk)
		{
		struct ns_common *nsc = &nsproxy->time_ns_for_children->ns;
		struct time_namespace *ns = to_time_ns(nsc);
		int err;

		/* create_new_namespaces() already incremented the ref counter */
		if (nsproxy->time_ns == nsproxy->time_ns_for_children)
		@@ -321,9 +317,7 @@ int timens_on_fork(struct nsproxy nsproxy, struct task_struct tsk)

		timens_set_vvar_page(tsk, ns);

		err = vdso_join_timens(tsk, ns);
		if (err)
		return err;
		vdso_join_timens(tsk, ns);

		get_time_ns(ns);
		put_time_ns(nsproxy->time_ns);

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