netdev - Re: [PATCH net] sctp: walk the list of asoc safely

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Message-ID: <20190201144359.GA9864@kroah.com>
Date:   Fri, 1 Feb 2019 15:43:59 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
        vuln@...unia.com
Subject: Re: [PATCH net] sctp: walk the list of asoc safely

On Fri, Feb 01, 2019 at 12:20:37PM -0200, Marcelo Ricardo Leitner wrote:
> On Fri, Feb 01, 2019 at 03:15:22PM +0100, Greg Kroah-Hartman wrote:
> > In sctp_sendmesg(), when walking the list of endpoint associations, the
> > association can be dropped from the list, making the list corrupt.
> > Properly handle this by using list_for_each_entry_safe()
> > 
> > Fixes: 4910280503f3 ("sctp: add support for snd flag SCTP_SENDALL process in sendmsg")
> > Reported-by: Secunia Research <vuln@...unia.com>
> > Tested-by: Secunia Research <vuln@...unia.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > 
> > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > index f93c3cf9e567..65d6d04546ae 100644
> > --- a/net/sctp/socket.c
> > +++ b/net/sctp/socket.c
> > @@ -2027,7 +2027,7 @@ static int sctp_sendmsg(struct sock *sk, struct msghdr *msg, size_t msg_len)
> >  	struct sctp_endpoint *ep = sctp_sk(sk)->ep;
> >  	struct sctp_transport *transport = NULL;
> >  	struct sctp_sndrcvinfo _sinfo, *sinfo;
> > -	struct sctp_association *asoc;
> > +	struct sctp_association *asoc, *tmp;
> >  	struct sctp_cmsgs cmsgs;
> >  	union sctp_addr *daddr;
> >  	bool new = false;
> > @@ -2053,7 +2053,7 @@ static int sctp_sendmsg(struct sock *sk, struct msghdr *msg, size_t msg_len)
> 
> Extending the context here by 1 line:
>         lock_sock(sk);
> >  
> >  	/* SCTP_SENDALL process */
> >  	if ((sflags & SCTP_SENDALL) && sctp_style(sk, UDP)) {
> > -		list_for_each_entry(asoc, &ep->asocs, asocs) {
> > +		list_for_each_entry_safe(asoc, tmp, &ep->asocs, asocs) {
> 
> With the socket being locked by here, how can an asoc be removed
> while the list is being traversed? The socket lock should be
> protecting from it.

What about when the SCTP_ABORT flag is set with SCTP_SENDALL at the same
time?

:(