Re: [Linux-stable-mirror] [PATCH AUTOSEL for 4.14 019/110] sctp: fix the issue that a __u16 variable may overflow in sctp_ulpq_renege

From: Xin Long

Sent: 06 February 2018 10:43 To: David Laight

On Mon, Feb 5, 2018 at 7:35 PM, David Laight David.Laight@aculab.com wrote:

...

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@gmail.com Signed-off-by: Xin Long lucien.xin@gmail.com Acked-by: Neil Horman nhorman@tuxdriver.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin alexander.levin@microsoft.com

---

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....

You meant 'if (u32 >= u16)' is not good ? If so, I did some tests:

# x.c int main() { unsigned int a = 1; unsigned short b = 1;

if (a > b) <---- a++; }

# y.c int main() { unsigned int a = 1; unsigned int b = 1;

if (a > b) <---- a++; }

# x.s movl $1, -4(%rbp) movw $1, -6(%rbp) movzwl -6(%rbp), %eax cmpl -4(%rbp), %eax

# y.s movl $1, -4(%rbp) movl $1, -8(%rbp) movl -4(%rbp), %eax cmpl -8(%rbp), %eax

So looks like x.c vs y.c is: movzwl vs movl

does it matter?

Compile it for something other than x86.

David