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

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Message-ID: <4ba6d2eb-972d-4e2e-7876-7ecf3e29a438@canonical.com>
Date:   Fri, 20 Jan 2017 13:15:18 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.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 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.

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