[OpenWrt-Devel] [PATCH v2] ubus: use network order in ubus message header fields

[Felix Fietkau]

On 2016-02-15 12:54, Eyal Birger wrote:
>     >     >       if (offset < sizeof(ub->hdr)) {
>     >     > -             iov[0].iov_base = ((char *) &ub->hdr) + offset;
>     >     > -             iov[0].iov_len = sizeof(ub->hdr) - offset;
>     >     > +             struct ubus_msghdr hdr;
>     >     > +
>     >     > +             hdr.version = ub->hdr.version;
>     >     > +             hdr.type = ub->hdr.type;
>     >     > +             hdr.seq = cpu_to_be16(ub->hdr.seq);
>     >     > +             hdr.peer = cpu_to_be32(ub->hdr.peer);
>     >     > +
>     >     > +             iov[0].iov_base = ((char *) &hdr) + offset;
>     >     > +             iov[0].iov_len = sizeof(hdr) - offset;
>     The corner case is this: You changed the iov to point at stack space
>     instead of ub->hdr. If the code receives a part of the header in one
>     call, and another one in the next (offset > 0), the contents of hdr will
>     be corrupt, as it will be a mix of uninitialized stack space + the
>     received data from the last call.
> Interesting... I initialize the iov_base every time to a newly created and
> calculated hdr variable before the sendmsg() call, and iov is never used
> otherwise - so I wonder how it could be reused in subsequent calls?
Before your change, iov[0].iov_base points at ub->hdr, which is on heap
and is preserved across calls.
After your change, iov[0].iov_base points at the on-stack struct hdr,
which is not preserved across calls.

- Felix
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