From: Al Viro <viro@zeniv.linux.org.uk>
To: Pan Bian <bianpan2016@163.com>
Cc: Amir Goldstein <amir73il@gmail.com>,
Miklos Szeredi <mszeredi@redhat.com>,
"J. Bruce Fields" <bfields@fieldses.org>,
Christoph Hellwig <hch@lst.de>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH V2] exportfs: do not read dentry after free
Date: Fri, 23 Nov 2018 14:07:22 +0000 [thread overview]
Message-ID: <20181123140722.GA2217@ZenIV.linux.org.uk> (raw)
In-Reply-To: <1542959793-118334-1-git-send-email-bianpan2016@163.com>
On Fri, Nov 23, 2018 at 03:56:33PM +0800, Pan Bian wrote:
> The function dentry_connected calls dput(dentry) to drop the previously
> acquired reference to dentry. In this case, dentry can be released.
> After that, IS_ROOT(dentry) checks the condition
> (dentry == dentry->d_parent), which may result in a use-after-free bug.
> This patch directly compares dentry with its parent obtained before
> dropping the reference.
It's a bit more subtle than the description implies (the race has
dentry connected during dget_parent() and the child we'd reached it
through moved elsewhere during the dput()), but you are right - the
race is there and that patch fixes it.
I wonder if we could avoid those dget_parent()/dput() completely -
looks like we might be able to with rcu_read_lock() and some
care. OTOH, that's not going to be a hot path, anyway...
Applied.
next prev parent reply other threads:[~2018-11-23 14:07 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-23 7:56 [PATCH V2] exportfs: do not read dentry after free Pan Bian
2018-11-23 14:07 ` Al Viro [this message]
2018-11-24 3:48 ` J. Bruce Fields
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