Re: [PATCH net] tipc: Guard against tiny MTU in tipc_msg_build()

On Thu, 2016-10-20 at 14:51 +0000, Jon Maloy wrote:
[...]

quoted

At this point we're about to copy INT_H_SIZE + mhsz bytes into the
first fragment.  If that's already limited to be less than or equal to
MAX_H_SIZE, comparing with MAX_H_SIZE would be fine.  But if MAX_H_SIZE
is the maximum value of mhsz, that won't be good enough.

MAX_H_SIZE is 60 bytes, but in practice you will never see an mhsz larger than the biggest header we are actually using, which is MCAST_H_SIZE (==44 bytes).
INT_H_SIZE is 40 bytes, so you are in reality testing for whether we have an mtu < 84 bytes.
You won't find any interfaces or protocols that come even close to this limitation, so to me this test is redundant.

But I can easily create such an interface:

$ unshare -n -U -r
# ip l set lo mtu 1

Ben.

-- 
Ben Hutchings
Never put off till tomorrow what you can avoid all together.