Commit 7ae8fd03 authored Feb 16, 2016 by Maxim Patlasov Committed by Al Viro Feb 20, 2016

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



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@virtuozzo.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

parent 0bacbe52

fs/pnode.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -202,6 +202,11 @@ static struct mount last_dest, last_source, *dest_master;
		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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