Date Wed, 28 Oct 2015 18:39:56 +0900 Subject Re: [GIT] Networking From Linus Torvalds <> On Wed, Oct 28, 2015 at 3:32 PM, David Miller <davem@davemloft.net> wrote:

>

> This may look a bit scary this late in the release cycle, but as is typically

> the case it's predominantly small driver fixes all over the place.



Christ people. This is just sh*t.



The conflict I get is due to stupid new gcc header file crap. But what

makes me upset is that the crap is for completely bogus reasons.



This is the old code in net/ipv6/ip6_output.c:



mtu -= hlen + sizeof(struct frag_hdr);



and this is the new "improved" code that uses fancy stuff that wants

magical built-in compiler support and has silly wrapper functions for

when it doesn't exist:



if (overflow_usub(mtu, hlen + sizeof(struct frag_hdr), &mtu) ||

mtu <= 7)

goto fail_toobig;



and anybody who thinks that the above is



(a) legible

(b) efficient (even with the magical compiler support)

(c) particularly safe



is just incompetent and out to lunch.



The above code is sh*t, and it generates shit code. It looks bad, and

there's no reason for it.



The code could *easily* have been done with just a single and

understandable conditional, and the compiler would actually have

generated better code, and the code would look better and more

understandable. Why is this not



if (mtu < hlen + sizeof(struct frag_hdr) + 8)

goto fail_toobig;

mtu -= hlen + sizeof(struct frag_hdr);



which is the same number of lines, doesn't use crazy helper functions

that nobody knows what they do, and is much more obvious what it

actually does.



I guarantee that the second more obvious version is easier to read and

understand. Does anybody really want to dispute this?



Really. Give me *one* reason why it was written in that idiotic way

with two different conditionals, and a shiny new nonstandard function

that wants particular compiler support to generate even half-way sane

code, and even then generates worse code? A shiny function that we

have never ever needed anywhere else, and that is just

compiler-masturbation.



And yes, you still could have overflow issues if the whole "hlen +

xyz" expression overflows, but quite frankly, the "overflow_usub()"

code had that too. So if you worry about that, then you damn well

didn't do the right thing to begin with.



So I really see no reason for this kind of complete idiotic crap.



Tell me why. Because I'm not pulling this kind of completely insane

stuff that generates conflicts at rc7 time, and that seems to have

absolutely no reason for being anm idiotic unreadable mess.



The code seems *designed* to use that new "overflow_usub()" code. It

seems to be an excuse to use that function.



And it's a f*cking bad excuse for that braindamage.



I'm sorry, but we don't add idiotic new interfaces like this for

idiotic new code like that.



Yes, yes, if this had stayed inside the network layer I would never

have noticed. But since I *did* notice, I really don't want to pull

this. In fact, I want to make it clear to *everybody* that code like

this is completely unacceptable. Anybody who thinks that code like

this is "safe" and "secure" because it uses fancy overflow detection

functions is so far out to lunch that it's not even funny. All this

kind of crap does is to make the code a unreadable mess with code that

no sane person will ever really understand what it actually does.



Get rid of it. And I don't *ever* want to see that shit again.



Linus





