Messages in this thread | | | From | Mike Frysinger <> | Date | Wed, 24 Jun 2009 07:35:12 -0400 | Subject | Re: [PATCH 1/4] asm-generic: uaccess: do not expand args multiple times |
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On Wed, Jun 24, 2009 at 00:38, Al Viro wrote: > On Sun, Jun 14, 2009 at 10:14:39PM +0200, Arnd Bergmann wrote: >> On Sunday 14 June 2009, Mike Frysinger wrote: >> > While it's debatable whether {get,put}_user() should be called with >> > arguments that have side effects, macro's should be written safely in the >> > first place. In this case, a slightly off version of put_user() ended up >> > causing random userspace corruption and these things aren't trivial to >> > track down. >> > >> > While some of these conversions aren't strictly necessary, I think it's >> > better to do all of them so as to be proactive in people accidently >> > screwing it up in the future. >> >> I've tried this and failed. This change adds an endless number of sparse >> warnings in put_user and even gcc warnings in get_user. The problem >> is that typeof() carries over the 'const' and '__user' modifiers, both >> of which prevent you from assigning data to the new pointer that you >> constructed. >> >> I'd love to see a way to do this correctly, but this patch won't cut it. > > Note that sizeof(*(ptr)) does *NOT* evaluate ptr, unless we are dealing > with variably-modified type. The same goes for typeof. And chk_user_ptr() > expands to (void)0 during the build.
i never said it does -- i explicitly said i converted more than needed on purpose
> So I don't believe that existing variant > is incorrect - we do not evaluate the argument twice.
except that it does. read get_user() where the argument is expanded once for access_ok() and twice when tailing to __get_user(). same goes for put_user(). -mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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