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authorAl Viro <viro@zeniv.linux.org.uk>2016-06-07 21:26:55 -0400
committerSasha Levin <sasha.levin@oracle.com>2016-06-19 23:47:45 -0400
commit34558d3f213b5d95253aba97b529d46f20b757cb (patch)
tree348cc05eb58b30c998c2cbd120c74a39fb0ad95b
parentd05438b3ba85517631b5ea2e1c88172f84dffe8b (diff)
downloadlinux-linaro-stable-34558d3f213b5d95253aba97b529d46f20b757cb.tar.gz
fix d_walk()/non-delayed __d_free() race
[ Upstream commit 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 ] 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. Cc: stable@vger.kernel.org # v3.2+ (and watch out for __d_materialise_dentry()) Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
-rw-r--r--fs/dcache.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/dcache.c b/fs/dcache.c
index d25f8fdcd397..7654509f398f 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1481,7 +1481,7 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
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
@@ -2313,7 +2313,6 @@ static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
{
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);
}
@@ -2532,6 +2531,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
/* ... 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);