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

[Rich Felker <dalias@libc.org>]

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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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diff --git a/src/signal/block.c b/src/signal/block.c
index d7f61001..cc8698f0 100644
--- a/src/signal/block.c
+++ b/src/signal/block.c
@@ -3,9 +3,9 @@
 #include <signal.h>
 
 static const unsigned long all_mask[] = {
-#if ULONG_MAX == 0xffffffff && _NSIG == 129
+#if ULONG_MAX == 0xffffffff && _NSIG > 65
 	-1UL, -1UL, -1UL, -1UL
-#elif ULONG_MAX == 0xffffffff
+#elif ULONG_MAX == 0xffffffff || _NSIG > 65
 	-1UL, -1UL
 #else
 	-1UL