netdev - Re: [PATCH] INET: fix incorrect "inet_sock->is

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Date:	Fri, 5 Jan 2007 00:32:31 -0200
From:	"Arnaldo Carvalho de Melo" <arnaldo.melo@...il.com>
To:	"David Miller" <davem@...emloft.net>
Cc:	paul.moore@...com, netdev@...r.kernel.org
Subject: Re: [PATCH] INET: fix incorrect "inet_sock->is_icsk" assignment

On 1/4/07, David Miller <davem@...emloft.net> wrote:
> From: "Paul Moore" <paul.moore@...com>
> Date: Thu, 04 Jan 2007 15:04:31 -0500
>
> > From: Paul Moore <paul.moore@...com>
> >
> > The inet_create() and inet6_create() functions incorrectly set the
> > inet_sock->is_icsk field.  Both functions assume that the is_icsk field is
> > large enough to hold at least a INET_PROTOSW_ICSK value when it is actually
> > only a single bit.  This patch corrects the assignment by doing a boolean
> > comparison whose result will safely fit into a single bit field.
> >
> > Signed-off-by: Paul Moore <paul.moore@...com>
>
> Applied, thanks a lot Paul.

Well spotted, gcc let me down on this one:

[acme@...toy ~]$ cat a.c
#include <stdio.h>

struct foo { int a_bit:1; };

int main(void) {
        int trickme = 0x04;
        struct foo oof;

        oof.a_bit = trickme & 4;
        printf("%u\n", oof.a_bit);
}
[acme@...toy ~]$ make a
cc     a.c   -o a
[acme@...toy ~]$ ./a
0
[acme@...toy ~]$

But...

[acme@...toy ~]$ cat a.c
#include <stdio.h>

struct foo { int a_bit:1; };

int main(void) {
        struct foo oof;

        oof.a_bit = 0x04;
        printf("%u\n", oof.a_bit);
}
[acme@...toy ~]$ make a
cc     a.c   -o a
a.c: In function 'main':
a.c:8: warning: overflow in implicit constant conversion
[acme@...toy ~]$

I expected a warning since the and operation clearly could yield a
value that would overflow, just like in the constant case...

Anyway, thanks a lot Paul!

- Arnaldo
-
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