RE: [PATCH AUTOSEL for 4.14 019/110] sctp: fix the issue that a __u16 variable may overflow in sctp_ulpq_renege

[David Laight]

From: Sasha Levin
> Sent: 03 February 2018 18:01
> [ Upstream commit 5c468674d17056148da06218d4da5d04baf22eac ]
> 
> Now when reneging events in sctp_ulpq_renege(), the variable freed
> could be increased by a __u16 value twice while freed is of __u16
> type. It means freed may overflow at the second addition.
> 
> This patch is to fix it by using __u32 type for 'freed', while at
> it, also to remove 'if (chunk)' check, as all renege commands are
> generated in sctp_eat_data and it can't be NULL.
> 
> Reported-by: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
> Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
> Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
> ---
>  net/sctp/ulpqueue.c | 24 ++++++++----------------
>  1 file changed, 8 insertions(+), 16 deletions(-)
> 
> diff --git a/net/sctp/ulpqueue.c b/net/sctp/ulpqueue.c
> index a71be33f3afe..e36ec5dd64c6 100644
> --- a/net/sctp/ulpqueue.c
> +++ b/net/sctp/ulpqueue.c
> @@ -1084,29 +1084,21 @@ void sctp_ulpq_partial_delivery(struct sctp_ulpq *ulpq,
>  void sctp_ulpq_renege(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
>  		      gfp_t gfp)
>  {
> -	struct sctp_association *asoc;
> -	__u16 needed, freed;
> -
> -	asoc = ulpq->asoc;
> +	struct sctp_association *asoc = ulpq->asoc;
> +	__u32 freed = 0;
> +	__u16 needed;
> 
> -	if (chunk) {
> -		needed = ntohs(chunk->chunk_hdr->length);
> -		needed -= sizeof(struct sctp_data_chunk);
> -	} else
> -		needed = SCTP_DEFAULT_MAXWINDOW;
> -
> -	freed = 0;
> +	needed = ntohs(chunk->chunk_hdr->length) -
> +		 sizeof(struct sctp_data_chunk);
> 
>  	if (skb_queue_empty(&asoc->base.sk->sk_receive_queue)) {
>  		freed = sctp_ulpq_renege_order(ulpq, needed);
> -		if (freed < needed) {
> +		if (freed < needed)
>  			freed += sctp_ulpq_renege_frags(ulpq, needed - freed);
> -		}
>  	}
>  	/* If able to free enough room, accept this chunk. */
> -	if (chunk && (freed >= needed)) {
> -		int retval;
> -		retval = sctp_ulpq_tail_data(ulpq, chunk, gfp);
> +	if (freed >= needed) {
> +		int retval = sctp_ulpq_tail_data(ulpq, chunk, gfp);
>  		/*
>  		 * Enter partial delivery if chunk has not been
>  		 * delivered; otherwise, drain the reassembly queue.

Hmmm...
ISTM that all the maths should be done using 'unsigned int' to avoid horrid
masking operations on many cpus....

	David