Commit 53c39433 authored Jun 01, 2016 by Jann Horn Committed by Min Chong Jul 25, 2016

UPSTREAM: proc: prevent stacking filesystems on top



(cherry picked from commit e54ad7f1ee263ffa5a2de9c609d58dfa27b21cd9)

This prevents stacking filesystems (ecryptfs and overlayfs) from using
procfs as lower filesystem.  There is too much magic going on inside
procfs, and there is no good reason to stack stuff on top of procfs.

(For example, procfs does access checks in VFS open handlers, and
ecryptfs by design calls open handlers from a kernel thread that doesn't
drop privileges or so.)

Signed-off-by: Jann Horn <jannh@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Change-Id: Ib050ef9dc10e623589d22e3a9e6aee9ee4f0cd5d
Bug: 29444228

parent f394c99b

fs/proc/root.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -121,6 +121,13 @@ static struct dentry proc_mount(struct file_system_type fs_type,
		if (IS_ERR(sb))
		return ERR_CAST(sb);

		/*
		* procfs isn't actually a stacking filesystem; however, there is
		* too much magic going on inside it to permit stacking things on
		* top of it
		*/
		sb->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;

		if (!proc_parse_options(options, ns)) {
		deactivate_locked_super(sb);
		return ERR_PTR(-EINVAL);