Re: [PATCH] sctp: don't dereference ptr before leaving _sctp_walk_{params,errors}()

From: Alexander Potapenko <glider@google.com>
Date: Thu, 13 Jul 2017 21:28:39 +0200

On Thu, Jul 13, 2017 at 8:32 PM, David Miller [off-list ref] wrote:

quoted

struct sctp_paramhdr {
        __be16 type;
        __be16 length;
};

typedef struct sctp_errhdr {
        __be16 cause;
        __be16 length;
        __u8  variable[0];
} sctp_errhdr_t;

 ...

quoted

Something like:

        pos.v + offsetof(pos.v, length) + sizeof(pos.v->length) <= (void *) chunk + end

Do we need to bother about truncated structures? Shouldn't it be
enough to check that there's at least sizeof(struct sctp_paramhdr)
bytes left then?

With the zero length array at the end, it's arguable what the "size"
of such a thing is.

That's why I tried to be explicit with the length field.