Re: [PATCH 06/10] ipc: Don't allocate a copy larger than max

[Peter Hurley]

On 05/25/2013 08:04 AM, Manfred Spraul wrote:
> Hi Peter,
>
> You wrote:
> > When MSG_COPY is set, a duplicate message must be allocated for
> > the copy before locking the queue. However, the copy could
> > not be larger than was sent which is limited to msg_ctlmax.
> >
> > Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
> > ---
> >   ipc/msg.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/ipc/msg.c b/ipc/msg.c
> > index 950572f..31cd1bf 100644
> > --- a/ipc/msg.c
> > +++ b/ipc/msg.c
> > @@ -820,15 +820,17 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
> >       struct msg_msg *copy = NULL;
> >       unsigned long copy_number = 0;
> > +    ns = current->nsproxy->ipc_ns;
> > +
> >       if (msqid < 0 || (long) bufsz < 0)
> >           return -EINVAL;
> >       if (msgflg & MSG_COPY) {
> > -        copy = prepare_copy(buf, bufsz, msgflg, &msgtyp, &copy_number);
> > +        copy = prepare_copy(buf, min_t(size_t, bufsz, ns->msg_ctlmax),
> > +                    msgflg, &msgtyp, &copy_number);
>
> What about:
> - increase msg_ctlmax
> - send message
> - reduce msg_ctlmax
>
> The side effects of the patch are odd:
> - without MSG_COPY, a message can be read regardsless of the size.
>    The user could check for E2BIG and increase the buffer size until
>    msgrcv succeeds.

The patch does not change the behavior of non-MSG_COPY msg receive.

> - with MSG_COPY, something else would happen.
>    As far as I can see, it would oops: msg_ctlmax bytes are allocated,
>    then the E2BIG test is against bufsz, and copy_msg() doesn't check
>    the size of the target buffer.

I assume you are using 3.9

Current mainline returns EINVAL.

Regards,
Peter Hurley
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