Patch "proc: prevent stacking filesystems on top" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

proc: prevent stacking filesystems on top

to the 3.14-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:
proc-prevent-stacking-filesystems-on-top.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jann Horn <[email protected]>
Date: Wed, 1 Jun 2016 11:55:05 +0200
Subject: proc: prevent stacking filesystems on top

From: Jann Horn <[email protected]>

commit e54ad7f1ee263ffa5a2de9c609d58dfa27b21cd9 upstream.

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.)

---
 fs/proc/root.c |    7 +++++++
 1 file changed, 7 insertions(+)

@@ -122,6 +122,13 @@ static struct dentry *proc_mount(struct
 	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);

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/ecryptfs-forbid-opening-files-without-mmap-handler.patch queue-3.14/proc-prevent-stacking-filesystems-on-top.patch