4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Maxim Patlasov <mpatlasov@xxxxxxxxxxxxx>
commit 7ae8fd0351f912b075149a1e03a017be8b903b9a upstream.
propagate_one(m) calculates "type" argument for copy_tree() like this:
> if (m->mnt_group_id == last_dest->mnt_group_id) {
> type = CL_MAKE_SHARED;
> } else {
> type = CL_SLAVE;
> if (IS_MNT_SHARED(m))
> type |= CL_MAKE_SHARED;
> }
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:
> last_source = last_source->mnt_master;
> last_dest = last_source->mnt_parent;
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...]
Signed-off-by: Maxim Patlasov <mpatlasov@xxxxxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/pnode.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -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;
}
--
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