linux-kernel - Re: [PATCH v2 1/2] sctp: export sctp_endpoint_{hold,put}() and return incremented endpoint

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: <20211217070626.790b8340@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 17 Dec 2021 07:06:26 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     linux-kernel@...r.kernel.org, Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        lksctp developers <linux-sctp@...r.kernel.org>,
        "H.P. Yarroll" <piggy@....org>,
        Karl Knutson <karl@...ena.chicago.il.us>,
        Jon Grimm <jgrimm@...ibm.com>,
        Xingang Guo <xingang.guo@...el.com>,
        Hui Huang <hui.huang@...ia.com>,
        Sridhar Samudrala <sri@...ibm.com>,
        Daisy Chang <daisyc@...ibm.com>,
        Ryan Layer <rmlayer@...ibm.com>,
        Kevin Gao <kevin.gao@...el.com>, netdev@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] sctp: export sctp_endpoint_{hold,put}() and
 return incremented endpoint

On Fri, 17 Dec 2021 13:46:06 +0000 Lee Jones wrote:
> For example, in sctp_sock_dump(), we could have the following hunk:
> 
> 	sctp_endpoint_hold(tsp->asoc->ep);
> 	ep = tsp->asoc->ep;
> 	sk = ep->base.sk
> 	lock_sock(ep->base.sk);
> 
> It is possible for this task to be swapped out immediately following
> the call into sctp_endpoint_hold() that would change the address of
> tsp->asoc->ep to point to a completely different endpoint.  This means
> a reference could be taken to the old endpoint and the new one would
> be processed without a reference taken, moreover the new endpoint
> could then be freed whilst still processing as a result, causing a
> use-after-free.
> 
> If we return the exact pointer that was held, we ensure this task
> processes only the endpoint we have taken a reference to.  The
> resultant hunk now looks like this:
> 
>       ep = sctp_endpoint_hold(tsp->asoc->ep);
> 	sk = ep->base.sk
> 	lock_sock(sk);

If you have to explain what the next patch will do to make sense 
of this one it really is better to merge the two patches.
Exporting something is not a functional change, nor does it make
the changes easier to review, in fact the opposite is true.

> Fixes: 8f840e47f190c ("sctp: add the sctp_diag.c file")

This patch in itself fixes exactly nothing.