On Thu, Apr 26, 2018 at 04:58:52PM -0300, Marcelo Ricardo Leitner wrote:
> As noticed by Xin Long, the if() here is always true as PMTU can never
> be 0.
>
> Reported-by: Xin Long <lucien.xin@xxxxxxxxx>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
> ---
> net/sctp/associola.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index b3aa95222bd52113295cb246c503c903bdd5c353..c5ed09cfa8423b17546e3d45f6d06db03af66384 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1397,10 +1397,8 @@ void sctp_assoc_sync_pmtu(struct sctp_association *asoc)
> pmtu = t->pathmtu;
> }
>
> - if (pmtu) {
> - asoc->pathmtu = pmtu;
> - asoc->frag_point = sctp_frag_point(asoc, pmtu);
> - }
> + asoc->pathmtu = pmtu;
> + asoc->frag_point = sctp_frag_point(asoc, pmtu);
>
Can you double check this? Looking at it, it seems far fetched, but if someone
sends a crafted icmp dest unreach message to the host, pmtu_sending might be
able to get set for an association (which may have no transports established
yet), and if so, on the first packet send sctp_assoc_sync_pmtu can be called,
leading to a fall through in the loop over all transports, and pmtu being zero.
It seems like a far fetched set of circumstances, I know, but if it can happen,
I think you might see a crash in sctp_frag_point due to an underflow of the frag
value
Neil
> pr_debug("%s: asoc:%p, pmtu:%d, frag_point:%d\n", __func__, asoc,
> asoc->pathmtu, asoc->frag_point);
> --
> 2.14.3
>
>
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