Re: Broken commit: [NETFILTER]: ipt_REJECT: remove largely duplicate route_reverse function

Patrick McHardy [off-list ref] writes:

It might be the case that your network device has a
hard_header_len > LL_MAX_HEADER, which could trigger
a corruption.

Hmm... GRE tunnels add 24 bytes... I just noticed the following code in
include/linux/netdevice.h:

/*
 *      Compute the worst case header length according to the protocols
 *      used.
 */
 
#if !defined(CONFIG_AX25) && !defined(CONFIG_AX25_MODULE) && !defined(CONFIG_TR)
#define LL_MAX_HEADER   32
#else
#if defined(CONFIG_AX25) || defined(CONFIG_AX25_MODULE)
#define LL_MAX_HEADER   96
#else
#define LL_MAX_HEADER   48
#endif
#endif

#if !defined(CONFIG_NET_IPIP) && \
    !defined(CONFIG_IPV6) && !defined(CONFIG_IPV6_MODULE)
#define MAX_HEADER LL_MAX_HEADER
#else
#define MAX_HEADER (LL_MAX_HEADER + 48)
#endif

I don't use AX25, Token Ring, the old IPIP tunnels nor IPv6 here, but
I wonder if GRE tunnel (which is basically another, more compatible
form of IPIP) need the same treatment as IPIP.

I've confirmed that REJECTs over GRE tunnel caused that corruption.

Please try this patch on top of the REJECT patch (ideally after
verifying that the REJECT patch is really introducing the
corruption).

That was certain. The patch fixed the problem, confirmed with current
git tree as well. Thanks for looking at it.


I'm not sure about LL_MAX_HEADER (and/or MAX_HEADER) though. Should it
be changed as well?

There are many devices adding data to header space, perhaps tacking
devices doesn't count as the skb is being linearized in
dev->hard_start_xmit() or equivalent path?
-- 
Krzysztof Halasa