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@xxxxxxxxxxxxxxx> know about it.
>From 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Tue, 7 Jun 2016 21:26:55 -0400
Subject: fix d_walk()/non-delayed __d_free() race
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxxxxxxxxxx are
queue-4.6/fix-d_walk-non-delayed-__d_free-race.patch
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