linux-kernel - Re: [PATCH] [suggestion] mm/gup: avoid IS_ERR_OR

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZGf1hV7iEQyqAim5@ziepe.ca>
Date:   Fri, 19 May 2023 19:17:41 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lorenzo Stoakes <lstoakes@...il.com>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] [suggestion] mm/gup: avoid IS_ERR_OR_NULL

On Fri, May 19, 2023 at 03:51:51PM +0100, Lorenzo Stoakes wrote:
> Given you are sharply criticising the code I authored here, is it too much
> to ask for you to cc- me, the author on commentaries like this? Thanks.
> 
> On Fri, May 19, 2023 at 11:39:13AM +0200, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > While looking at an unused-variable warning, I noticed a new interface coming
> > in that requires the use of IS_ERR_OR_NULL(), which tends to indicate bad
> > interface design and is usually surprising to users.
> 
> I am not sure I understand your reasoning, why does it 'tend to indicate
> bad interface design'? You say that as if it is an obvious truth. Not
> obvious to me at all.
>
> There are 3 possible outcomes from the function - an error, the function
> failing to pin a page, or it succeeding in doing so. For some of the
> callers that results in an error, for others it is not an error.

No, there really isn't.

Either it pins the page or it doesn't. Returning "NULL" to mean a
specific kind of failure was encountered is crazy.. Especially if we
don't document what that specific failure even was.

IIRC if you look really closely the only time get_user_pages()
actually returns 0 is if the input argument validation fails, which I
think is a bug that should be fixed.

get_user_pages() never returns 0, so get_user_page_vma_remote() never
returns NULL. Until we get there collapsing the 0 to EIO is perfectly
fine.

Jason