linux-kernel - Re: [PATCH] pipe: fix potential use-after-free in pipe

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Y4Bh0fTf4vZ6/6Pc@ZenIV>
Date:   Fri, 25 Nov 2022 06:33:53 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Howells <dhowells@...hat.com>
Subject: Re: [PATCH] pipe: fix potential use-after-free in pipe_read()

On Thu, Nov 17, 2022 at 07:53:23PM +0800, Zhen Lei wrote:
> Accessing buf->flags after pipe_buf_release(pipe, buf) is unsafe, because
> the 'buf' memory maybe freed.

Huh?  What are you talking about?
                        struct pipe_buffer *buf = &pipe->bufs[tail & mask];
To free *buf you would need to free the entire damn array, which is
obviously not going to be possible here; if you are talking about reuse
of *buf - that's controlled by pipe->tail, and we do not assign it until
later.

Fetching any fields of *buf is safe; what can get freed is buf->page, not
buf itself.  So that buf->flags access is fine.