Re: [musl] Bug in src/signal/block.c

[Jasper Hugunin <jasper@hugunin.net>]

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It looks ok to me, I think that will work for all the architectures
currently around.

I do worry about what would happen on an architecture setting `_NSIG` to
something other than 65 or 128, say 256 or 230 or something like that, but
that is a larger scale concern for the whole musl codebase.

(Note: I am not an expert on signal handling, I was just poking around the
code when I spotted this inconsistency.)

Sincerely,
- Jasper Hugunin

On Wed, Jul 28, 2021 at 12:36 PM Rich Felker <dalias@libc.org> wrote:

> On Wed, Jul 28, 2021 at 11:53:41AM -0400, Rich Felker wrote:
> > On Wed, Jul 28, 2021 at 08:00:00AM -0700, Jasper Hugunin wrote:
> > > Hello,
> > >
> > > In musl, as far as I can tell, `_NSIG` is always defined as either 65,
> or
> > > 128 (for all three MIPS architectures) at the bottom of
> > > `${arch}/bits/signal.h`. Meanwhile, in `src/signal/block.c`, there is a
> > > test `#if ULONG_MAX == 0xffffffff && _NSIG == 129`, which will never
> > > succeed since _NSIG will be 128 instead of 129. This seems likely to be
> > > left over from Commit: fix _NSIG and SIGRTMAX on mips
> > > <
> https://git.musl-libc.org/cgit/musl/commit/arch?id=7c440977db9444d7e6b1c3dcb1fdf4ee49ca4158
> >
> > > ..
> > >
> > > I have not demonstrated the bug, I found it by inspection of the
> source. My
> > > guess is that this bug causes __block_all_sigs to fail to block high
> real
> > > time signals on MIPS. At best, however, this test seems to be dead
> code.
> > >
> > > (I am not subscribed to the mailing list; please cc me directly on any
> > > responses I need to see.)
> > > My apologies if I have misunderstood the situation.
> >
> > Thanks! This is a real bug that will prevent signal blocking from
> > working correctly on mips, resulting in application code being able to
> > run in contexts where it is unsafe for that to happen if the
> > application installs signal handlers on high signal numbers.
>
> Does the attached patch look ok?
>
> Rich
>

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