Commit 4afddd60 authored Apr 02, 2014 by Tejun Heo Committed by Greg Kroah-Hartman Apr 16, 2014

kernfs: protect lazy kernfs_iattrs allocation with mutex



kernfs_iattrs is allocated lazily when operations which require it
take place; unfortunately, the lazy allocation and returning weren't
properly synchronized and when there are multiple concurrent
operations, it might end up returning kernfs_iattrs which hasn't
finished initialization yet or different copies to different callers.

Fix it by synchronizing with a mutex.  This can be smarter with memory
barriers but let's go there if it actually turns out to be necessary.

Signed-off-by: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/g/533ABA32.9080602@oracle.com


Reported-by: Sasha Levin <sasha.levin@oracle.com>
Cc: stable@vger.kernel.org # 3.14
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent a2a4dc49

fs/kernfs/inode.c

+10 −4

Original line number	Diff line number	Diff line
		@@ -48,14 +48,18 @@ void __init kernfs_inode_init(void)

		static struct kernfs_iattrs kernfs_iattrs(struct kernfs_node kn)
		{
		static DEFINE_MUTEX(iattr_mutex);
		struct kernfs_iattrs *ret;
		struct iattr *iattrs;

		mutex_lock(&iattr_mutex);

		if (kn->iattr)
		return kn->iattr;
		goto out_unlock;

		kn->iattr = kzalloc(sizeof(struct kernfs_iattrs), GFP_KERNEL);
		if (!kn->iattr)
		return NULL;
		goto out_unlock;
		iattrs = &kn->iattr->ia_iattr;

		/* assign default attributes */
		@@ -65,8 +69,10 @@ static struct kernfs_iattrs kernfs_iattrs(struct kernfs_node kn)
		iattrs->ia_atime = iattrs->ia_mtime = iattrs->ia_ctime = CURRENT_TIME;

		simple_xattrs_init(&kn->iattr->xattrs);

		return kn->iattr;
		out_unlock:
		ret = kn->iattr;
		mutex_unlock(&iattr_mutex);
		return ret;
		}

		static int __kernfs_setattr(struct kernfs_node kn, const struct iattr iattr)