On Sat, 2 Nov 2013, Adrian Chadd wrote:
Log:
Teach the netgraph code to use a const char * pointer too.
This actually fixes a much larger bug that was apparently accidentally
exposed by new const poisoning and new smaller type bugs.
Pointy hat to: adrian
Outpointed by the previous bug.
Modified: head/sys/netgraph/ng_iface.c
==============================================================================
--- head/sys/netgraph/ng_iface.c Fri Nov 1 23:30:54 2013
(r257534)
+++ head/sys/netgraph/ng_iface.c Sat Nov 2 00:11:38 2013
(r257535)
@@ -776,7 +776,7 @@ ng_iface_rcvdata(hook_p hook, item_p ite
return (EAFNOSUPPORT);
}
if (harvest.point_to_point)
- random_harvest(&(m->m_data), 12, 2, RANDOM_NET_NG);
'&(m->m_data)' is not just a pair of style bugs. It gives address of
the pointer (somewhere in the mbuf header), not the address of pointed-
to data, so the randomness was almost null. The style bugs are
excessive parentheses and chumminess with the implementation (non-use
of the accessor function mtod()).
+ random_harvest(mtod(m, const void *), 12, 2, RANDOM_NET_NG);
Presumably you really do want to harvest the pointed-to data and there
are at least 12 bytes of it, so the semantic fix isn't backwards or a
buffer overrun.
M_SETFIB(m, ifp->if_fib);
netisr_dispatch(isr, m);
return (0);
const poisoning sometimes exposes garbage pointers accidentally. It seems
to take a new design error (random_harvest() taking a const char * instead
of a const void *) for this bug to be detected. random_harvest() used to
take a void * arg and the garbage pointer was automatically converted to
that. Conversion to const void * would be just as automatic.
The log message says const char * but the code says const void *. The
latter is correct, at least mtod() is used, since the mtod() API
unfortunately requires naming a type and const void * is the best type
to use here. Then futher conversions apparently occur: if there is
actually a const char * anywhere, it is wrong, and if we convert this
const void * to it then we must convert to const u_char * to actually
access the data It is best for intermediate conversions to only go
through const void * and not expand the old design error of making them
go through caddr_t (for m_data).
Bruce
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