netdev - Re: [PATCH] net: sctp: fix array overrun read on sctp_timer

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Date:   Fri, 20 Jan 2017 11:22:02 -0200
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Colin Ian King <colin.king@...onical.com>
Cc:     Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        "David S . Miller" <davem@...emloft.net>,
        linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, lucien.xin@...il.com
Subject: Re: [PATCH] net: sctp: fix array overrun read on sctp_timer_tbl

On Fri, Jan 20, 2017 at 01:15:18PM +0000, Colin Ian King wrote:
> On 20/01/17 13:10, Marcelo Ricardo Leitner wrote:
> > On Fri, Jan 20, 2017 at 01:01:57PM +0000, Colin King wrote:
> >> From: Colin Ian King <colin.king@...onical.com>
> >>
> >> The comparison on the timeout can lead to an array overrun
> >> read on sctp_timer_tbl because of an off-by-one error. Fix
> >> this by using < instead of <= and also compare to the array
> >> size rather than SCTP_EVENT_TIMEOUT_MAX.
> >>
> >> Fixes CoverityScan CID#1397639 ("Out-of-bounds read")
> >>
> >> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> >> ---
> >>  net/sctp/debug.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/net/sctp/debug.c b/net/sctp/debug.c
> >> index 95d7b15..e371a0d 100644
> >> --- a/net/sctp/debug.c
> >> +++ b/net/sctp/debug.c
> >> @@ -166,7 +166,7 @@ static const char *const sctp_timer_tbl[] = {
> >>  /* Lookup timer debug name. */
> >>  const char *sctp_tname(const sctp_subtype_t id)
> >>  {
> >> -	if (id.timeout <= SCTP_EVENT_TIMEOUT_MAX)
> >> +	if (id.timeout < ARRAY_SIZE(sctp_timer_tbl))
> >>  		return sctp_timer_tbl[id.timeout];
> > 
> > The issue exists but this is not the right fix.
> > Issue was introduced by 7b9438de0cd4 ("sctp: add stream reconf timer")
> > as it introduced a new timer but didn't add the timer name here, so the
> > fix should (also) include:
> > 
> > diff --git a/net/sctp/debug.c b/net/sctp/debug.c
> > index 95d7b15dad21..c5f4ed5242ac 100644
> > --- a/net/sctp/debug.c
> > +++ b/net/sctp/debug.c
> > @@ -159,6 +159,7 @@ static const char *const sctp_timer_tbl[] = {
> >  	"TIMEOUT_T4_RTO",
> >  	"TIMEOUT_T5_SHUTDOWN_GUARD",
> >  	"TIMEOUT_HEARTBEAT",
> > +	"TIMEOUT_RECONF",
> >  	"TIMEOUT_SACK",
> >  	"TIMEOUT_AUTOCLOSE",
> >  };
> 
> Ah, OK, I can add that timeout into the the table, but perhaps it's
> still prudent to check the index against the table size as well.
> 

Yes, and/or a:
  BUILD_BUG_ON(SCTP_EVENT_TIMEOUT_MAX + 1 != ARRAY_SIZE(sctp_timer_tbl))
As then we would be sure to have the list right :-)
Otherwise we may not do wrong reads but may report the wrong timer name.

> > 
> > Thanks,
> > Marcelo
> > 
> >>  	return "unknown_timer";
> >>  }
> >> -- 
> >> 2.10.2
> >>
> >> --
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> >>
> 
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