Patch "fix d_walk()/non-delayed __d_free() race" has been added to the 4.6-stable tree

Patch "fix d_walk()/non-delayed __d_free() race" has been added to the 4.6-stable tree

[gregkh]

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

    fix d_walk()/non-delayed __d_free() race

to the 4.6-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:
     fix-d_walk-non-delayed-__d_free-race.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue, 7 Jun 2016 21:26:55 -0400
Subject: fix d_walk()/non-delayed __d_free() race

From: Al Viro <viro@zeniv.linux.org.uk>

commit 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 upstream.

Ascend-to-parent logics in d_walk() depends on all encountered child
dentries not getting freed without an RCU delay.  Unfortunately, in
quite a few cases it is not true, with hard-to-hit oopsable race as
the result.

Fortunately, the fix is simiple; right now the rule is "if it ever
been hashed, freeing must be delayed" and changing it to "if it
ever had a parent, freeing must be delayed" closes that hole and
covers all cases the old rule used to cover.  Moreover, pipes and
sockets remain _not_ covered, so we do not introduce RCU delay in
the cases which are the reason for having that delay conditional
in the first place.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/dcache.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1619,7 +1619,7 @@ struct dentry *d_alloc(struct dentry * p
 	struct dentry *dentry = __d_alloc(parent->d_sb, name);
 	if (!dentry)
 		return NULL;
-
+	dentry->d_flags |= DCACHE_RCUACCESS;
 	spin_lock(&parent->d_lock);
 	/*
 	 * don't need child lock because it is not subject
@@ -2338,7 +2338,6 @@ static void __d_rehash(struct dentry * e
 {
 	BUG_ON(!d_unhashed(entry));
 	hlist_bl_lock(b);
-	entry->d_flags |= DCACHE_RCUACCESS;
 	hlist_bl_add_head_rcu(&entry->d_hash, b);
 	hlist_bl_unlock(b);
 }
@@ -2637,6 +2636,7 @@ static void __d_move(struct dentry *dent
 	/* ... and switch them in the tree */
 	if (IS_ROOT(dentry)) {
 		/* splicing a tree */
+		dentry->d_flags |= DCACHE_RCUACCESS;
 		dentry->d_parent = target->d_parent;
 		target->d_parent = target;
 		list_del_init(&target->d_child);


Patches currently in stable-queue which might be from viro@zeniv.linux.org.uk are

queue-4.6/fix-d_walk-non-delayed-__d_free-race.patch