Patch "fs/pnode.c: treat zero mnt_group_id-s as unequal" has been added to the 4.4-stable tree

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

fs/pnode.c: treat zero mnt_group_id-s as unequal

to the 4.4-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:
fs-pnode.c-treat-zero-mnt_group_id-s-as-unequal.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Maxim Patlasov <[email protected]>
Date: Tue, 16 Feb 2016 11:45:33 -0800
Subject: fs/pnode.c: treat zero mnt_group_id-s as unequal

From: Maxim Patlasov <[email protected]>

commit 7ae8fd0351f912b075149a1e03a017be8b903b9a upstream.

propagate_one(m) calculates "type" argument for copy_tree() like this:

The "type" argument then governs clone_mnt() behavior with respect to flags and mnt_master of new mount. When we iterate through a slave group, it is possible that both current "m" and "last_dest" are not shared (although, both are slaves, i.e. have non-NULL mnt_master-s). Then the comparison above erroneously makes new mount shared and sets its mnt_master to last_source->mnt_master. The patch fixes the problem by handling zero mnt_group_id-s as though they are unequal.

The similar problem exists in the implementation of "else" clause above when we have to ascend upward in the master/slave tree by calling:

proper number of times. The last step is governed by "n->mnt_group_id != last_dest->mnt_group_id" condition that may lie if both are zero. The patch fixes this case in the same way as the former one.

[AV: don't open-code an obvious helper...]

---
 fs/pnode.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

@@ -202,6 +202,11 @@ static struct mount *last_dest, *last_so
 static struct mountpoint *mp;
 static struct hlist_head *list;
 
+static inline bool peers(struct mount *m1, struct mount *m2)
+{
+	return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
+}
+
 static int propagate_one(struct mount *m)
 {
 	struct mount *child;

@@ -212,7 +217,7 @@ static int propagate_one(struct mount *m
 	/* skip if mountpoint isn't covered by it */
 	if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
 		return 0;
-	if (m->mnt_group_id == last_dest->mnt_group_id) {
+	if (peers(m, last_dest)) {
 		type = CL_MAKE_SHARED;
 	} else {
 		struct mount *n, *p;

@@ -223,7 +228,7 @@ static int propagate_one(struct mount *m
 					last_source = last_source->mnt_master;
 					last_dest = last_source->mnt_parent;
 				}
-				if (n->mnt_group_id != last_dest->mnt_group_id) {
+				if (!peers(n, last_dest)) {
 					last_source = last_source->mnt_master;
 					last_dest = last_source->mnt_parent;
 				}

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

queue-4.4/fs-pnode.c-treat-zero-mnt_group_id-s-as-unequal.patch