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From: Ralph Little <skelband@gmail.com>
To: musl@lists.openwall.com
Subject: Re: [musl] Re: [BUG] ioctl: overflow in implicit constant conversion
Date: Tue, 21 Feb 2023 10:25:05 -0800	[thread overview]
Message-ID: <CAFNXweO9EBZOjJXCicfaRJdZ=sffkstk98KyvY4X+Sw_tjZ03A@mail.gmail.com> (raw)
In-Reply-To: <CAH8yC8nTVCv_UWnm-NxYmo2ek66np9xOR4Mu7b1mQ63jU03ZdA@mail.gmail.com>

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Hi,

On Tue, Feb 21, 2023 at 8:58 AM Jeffrey Walton <noloader@gmail.com> wrote:

> On Tue, Feb 21, 2023 at 11:05 AM Markus Wichmann <nullplan@gmx.net> wrote:
> > On Mon, Feb 20, 2023 at 09:26:05PM -0800, Ralph Little wrote:
> > > I have been picking up some old pending issues related to the SANE
> project.
> > > One of our CI builds is on Alpine and it is generating warnings for
> ioctl()
> > > calls from the musl library:
> > >
> > > |error: overflow in conversion from 'long unsigned int' to 'int'
> changes
> > > value from '2147577985' to '-2147389311' [-Werror=overflow]
> > > |
> > > ||ioctl (fd, PPRSTATUS, &status);
> > >
> > > ||I see that Olaf Meeuwissen raised this issue a couple of years ago
> and the
> > > discussion petered out somewhat and I don't believe that the issue was
> ever
> > > really resolved:
> > >
> > > https://www.openwall.com/lists/musl/2020/01/20/2
> > >
> > > Is there any possibility that this could be addressed in the near
> future?
> > > I see that Alpine have closed their issue and are not interested in
> patching
> > > their downstream musl:
> > >
> > > https://gitlab.alpinelinux.org/alpine/aports/-/issues/7580#note_287168
> > [...]
> > So, I had a look at it. As far as I can tell, the issue is that musl
> > declares ioctl()'s second argument to be an int. Together with the other
> > defintions, this means that any _IOC_READ constant will overflow and
> > generate those warnings. Also, this is technically undefined behavior,
> > as value bits are shifted into the sign bit of a signed integer.
> >
> > Linux itself defines the ioctl syscall to have a second argument of type
> > unsigned int.
> >
> > So this issue could be resolved by simply making the second argument of
> > the ioctl() function unsigned. Does that create ABI issues? To my
> > knowledge, all ABIs pass ints and unsigned ints the same way. Even if on
> > some 64-bit arch there was a sign extension at the top, only the low
> > 32 bits are defined.
>
> In this case, I think the best course of action is to cast a,b,c to
> unsigned, then perform the shifts, and finally cast back to int. That
> is what the C standard requires. And it should not mess with the ABI.
>
> If the code remains undefined, then it is subject to removal by the
> compiler. The casts, while ugly, keep the code in well defined
> territory. Also, if anyone ever performs testing with
> -fsantize=undefined, then the code will trigger real findings that
> could keep the code from passing through a security gate (for those
> folks who have to work in that kind of environment).
>
> I've had to work bug reports that were a result of the missing casts
> during shifts and rotates. It is not fun. I was able to track all of
> them down with -fsantize=undefined .
>
> Jeff
>

That would be cool by me. I hate making macros complicated but I also
understand the POSIX issue.
Seems a shame that POSIX is so out of step these days with actual
implementations. Perhaps that will change in the future....

Cool to be reminded of the GCC santize settings. I had forgotten about
those.

Cheers,
Ralph

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  reply	other threads:[~2023-02-21 18:25 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-21  5:26 Ralph Little
2023-02-21 16:04 ` Markus Wichmann
2023-02-21 16:42   ` Florian Weimer
2023-02-21 16:53     ` alice
2023-02-21 16:57   ` Jeffrey Walton
2023-02-21 18:25     ` Ralph Little [this message]
2023-02-21 21:28     ` Markus Wichmann
2023-02-22  6:33       ` NRK
2023-02-22  3:17   ` Rich Felker
2023-02-22  4:23     ` Markus Wichmann
2023-02-22 15:53       ` Rich Felker

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