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* [musl] graceful nscd fallback on kernels without AF_UNIX support
@ 2021-04-03 10:58 Joakim Sindholt
  2021-04-03 14:42 ` Rich Felker
  0 siblings, 1 reply; 4+ messages in thread
From: Joakim Sindholt @ 2021-04-03 10:58 UTC (permalink / raw)
  To: musl

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I was reminded of this coincidentally on IRC and apparently it was never
applied, presumably because I never actually sent a proper patch.

5 years ago someone came in asking about musl on a system without
AF_UNIX support and this patch is what we came up with. It does require
access to /dev/null which might itself be a problem now that musl is
shedding filesystem requirements.

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From 9984ac4ad320844a91bbcdbc9f5fa07d3154621e Mon Sep 17 00:00:00 2001
From: Joakim Sindholt <opensource@zhasha.com>
Date: Sat, 3 Apr 2021 12:50:18 +0200
Subject: [PATCH] nscd: fall back gracefully on kernels without AF_UNIX support

---
 src/passwd/nscd_query.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/passwd/nscd_query.c b/src/passwd/nscd_query.c
index d38e371b..8641e4f0 100644
--- a/src/passwd/nscd_query.c
+++ b/src/passwd/nscd_query.c
@@ -40,7 +40,13 @@ retry:
 	buf[0] = NSCDVERSION;
 
 	fd = socket(PF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
-	if (fd < 0) return NULL;
+	if (fd < 0) {
+		if (errno == EACCES || errno == EAFNOSUPPORT || errno == EPROTONOSUPPORT) {
+			errno = errno_save;
+			return fopen("/dev/null", "re");
+		}
+		return 0;
+	}
 
 	if(!(f = fdopen(fd, "r"))) {
 		close(fd);
-- 
2.26.2


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [musl] graceful nscd fallback on kernels without AF_UNIX support
  2021-04-03 10:58 [musl] graceful nscd fallback on kernels without AF_UNIX support Joakim Sindholt
@ 2021-04-03 14:42 ` Rich Felker
  2021-04-03 15:03   ` Joakim Sindholt
  0 siblings, 1 reply; 4+ messages in thread
From: Rich Felker @ 2021-04-03 14:42 UTC (permalink / raw)
  To: Joakim Sindholt; +Cc: musl

On Sat, Apr 03, 2021 at 12:58:42PM +0200, Joakim Sindholt wrote:
> I was reminded of this coincidentally on IRC and apparently it was never
> applied, presumably because I never actually sent a proper patch.
> 
> 5 years ago someone came in asking about musl on a system without
> AF_UNIX support and this patch is what we came up with. It does require
> access to /dev/null which might itself be a problem now that musl is
> shedding filesystem requirements.

It's not really a problem, but it's also not necessary. fmemopen of an
empty buffer would also work, but might be undesirable for pulling in
more unnecessary code. So this is probably best as you wrote it:

> >From 9984ac4ad320844a91bbcdbc9f5fa07d3154621e Mon Sep 17 00:00:00 2001
> From: Joakim Sindholt <opensource@zhasha.com>
> Date: Sat, 3 Apr 2021 12:50:18 +0200
> Subject: [PATCH] nscd: fall back gracefully on kernels without AF_UNIX support
> 
> ---
>  src/passwd/nscd_query.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/src/passwd/nscd_query.c b/src/passwd/nscd_query.c
> index d38e371b..8641e4f0 100644
> --- a/src/passwd/nscd_query.c
> +++ b/src/passwd/nscd_query.c
> @@ -40,7 +40,13 @@ retry:
>  	buf[0] = NSCDVERSION;
>  
>  	fd = socket(PF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
> -	if (fd < 0) return NULL;
> +	if (fd < 0) {
> +		if (errno == EACCES || errno == EAFNOSUPPORT || errno == EPROTONOSUPPORT) {
> +			errno = errno_save;
> +			return fopen("/dev/null", "re");
> +		}
> +		return 0;
> +	}

What is the EACCESS case for here? EPROTONOSUPPORT is probably not
needed either (is it possible to have AF_UNIX supported but stream
mode support disabled?). Not a big deal but I'd rather not violate
YAGNI adding cases that don't have a legitimate reason to be possible.

Rich

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [musl] graceful nscd fallback on kernels without AF_UNIX support
  2021-04-03 14:42 ` Rich Felker
@ 2021-04-03 15:03   ` Joakim Sindholt
  2021-04-03 15:47     ` Rich Felker
  0 siblings, 1 reply; 4+ messages in thread
From: Joakim Sindholt @ 2021-04-03 15:03 UTC (permalink / raw)
  To: musl

On Sat, Apr 03, 2021 at 10:42:57AM -0400, Rich Felker wrote:
> On Sat, Apr 03, 2021 at 12:58:42PM +0200, Joakim Sindholt wrote:
> > I was reminded of this coincidentally on IRC and apparently it was never
> > applied, presumably because I never actually sent a proper patch.
> > 
> > 5 years ago someone came in asking about musl on a system without
> > AF_UNIX support and this patch is what we came up with. It does require
> > access to /dev/null which might itself be a problem now that musl is
> > shedding filesystem requirements.
> 
> It's not really a problem, but it's also not necessary. fmemopen of an
> empty buffer would also work, but might be undesirable for pulling in
> more unnecessary code. So this is probably best as you wrote it:

From the old chat logs it seems we both agreed that opening /dev/null
was preferable for the same reason.

> > >From 9984ac4ad320844a91bbcdbc9f5fa07d3154621e Mon Sep 17 00:00:00 2001
> > From: Joakim Sindholt <opensource@zhasha.com>
> > Date: Sat, 3 Apr 2021 12:50:18 +0200
> > Subject: [PATCH] nscd: fall back gracefully on kernels without AF_UNIX support
> > 
> > ---
> >  src/passwd/nscd_query.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/src/passwd/nscd_query.c b/src/passwd/nscd_query.c
> > index d38e371b..8641e4f0 100644
> > --- a/src/passwd/nscd_query.c
> > +++ b/src/passwd/nscd_query.c
> > @@ -40,7 +40,13 @@ retry:
> >  	buf[0] = NSCDVERSION;
> >  
> >  	fd = socket(PF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
> > -	if (fd < 0) return NULL;
> > +	if (fd < 0) {
> > +		if (errno == EACCES || errno == EAFNOSUPPORT || errno == EPROTONOSUPPORT) {
> > +			errno = errno_save;
> > +			return fopen("/dev/null", "re");
> > +		}
> > +		return 0;
> > +	}
> 
> What is the EACCESS case for here? EPROTONOSUPPORT is probably not
> needed either (is it possible to have AF_UNIX supported but stream
> mode support disabled?). Not a big deal but I'd rather not violate
> YAGNI adding cases that don't have a legitimate reason to be possible.

It's been so long that I can't remember. Best guess is that EACCES
allows it to fall back in a hypothetical container where it's not
allowed to call socket() but of course that should yield ENOSYS, a case
we might want to handle instead, and will probably yield EPERM in
current (last?) gen containers.
I probably got it from Linux Programmer's Manual which says:
EACCES  Permission to create a socket of the specified type and/or
        protocol is denied.
For what it's worth there's no mention of EACCES in net/unix and all
other non-protocol-specific EACCES seem to be unrelated to socket().

As for EPROTONOSUPPORT: I can't find any config option in linux that
disables stream/dgram/etc. Just CONFIG_UNIX that disables unix sockets
entirely.

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [musl] graceful nscd fallback on kernels without AF_UNIX support
  2021-04-03 15:03   ` Joakim Sindholt
@ 2021-04-03 15:47     ` Rich Felker
  0 siblings, 0 replies; 4+ messages in thread
From: Rich Felker @ 2021-04-03 15:47 UTC (permalink / raw)
  To: Joakim Sindholt; +Cc: musl

On Sat, Apr 03, 2021 at 05:03:55PM +0200, Joakim Sindholt wrote:
> On Sat, Apr 03, 2021 at 10:42:57AM -0400, Rich Felker wrote:
> > On Sat, Apr 03, 2021 at 12:58:42PM +0200, Joakim Sindholt wrote:
> > > I was reminded of this coincidentally on IRC and apparently it was never
> > > applied, presumably because I never actually sent a proper patch.
> > > 
> > > 5 years ago someone came in asking about musl on a system without
> > > AF_UNIX support and this patch is what we came up with. It does require
> > > access to /dev/null which might itself be a problem now that musl is
> > > shedding filesystem requirements.
> > 
> > It's not really a problem, but it's also not necessary. fmemopen of an
> > empty buffer would also work, but might be undesirable for pulling in
> > more unnecessary code. So this is probably best as you wrote it:
> 
> From the old chat logs it seems we both agreed that opening /dev/null
> was preferable for the same reason.

Ah, I'd forgotten we discussed it before, but yes that makes sense.

> > > >From 9984ac4ad320844a91bbcdbc9f5fa07d3154621e Mon Sep 17 00:00:00 2001
> > > From: Joakim Sindholt <opensource@zhasha.com>
> > > Date: Sat, 3 Apr 2021 12:50:18 +0200
> > > Subject: [PATCH] nscd: fall back gracefully on kernels without AF_UNIX support
> > > 
> > > ---
> > >  src/passwd/nscd_query.c | 8 +++++++-
> > >  1 file changed, 7 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/src/passwd/nscd_query.c b/src/passwd/nscd_query.c
> > > index d38e371b..8641e4f0 100644
> > > --- a/src/passwd/nscd_query.c
> > > +++ b/src/passwd/nscd_query.c
> > > @@ -40,7 +40,13 @@ retry:
> > >  	buf[0] = NSCDVERSION;
> > >  
> > >  	fd = socket(PF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
> > > -	if (fd < 0) return NULL;
> > > +	if (fd < 0) {
> > > +		if (errno == EACCES || errno == EAFNOSUPPORT || errno == EPROTONOSUPPORT) {
> > > +			errno = errno_save;
> > > +			return fopen("/dev/null", "re");
> > > +		}
> > > +		return 0;
> > > +	}
> > 
> > What is the EACCESS case for here? EPROTONOSUPPORT is probably not
> > needed either (is it possible to have AF_UNIX supported but stream
> > mode support disabled?). Not a big deal but I'd rather not violate
> > YAGNI adding cases that don't have a legitimate reason to be possible.
> 
> It's been so long that I can't remember. Best guess is that EACCES
> allows it to fall back in a hypothetical container where it's not
> allowed to call socket() but of course that should yield ENOSYS, a case
> we might want to handle instead, and will probably yield EPERM in
> current (last?) gen containers.
> I probably got it from Linux Programmer's Manual which says:
> EACCES  Permission to create a socket of the specified type and/or
>         protocol is denied.
> For what it's worth there's no mention of EACCES in net/unix and all
> other non-protocol-specific EACCES seem to be unrelated to socket().

Yes, I think EACCES is just for things like SOCK_RAW and IPPROTO_ICMP
where they're restricted because they fundamentally allow bypassing
the socket layer's model of address/service-port ownership.

> As for EPROTONOSUPPORT: I can't find any config option in linux that
> disables stream/dgram/etc. Just CONFIG_UNIX that disables unix sockets
> entirely.

Yeah. Let's just do EAFNOSUPPORT then.

Rich

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2021-04-03 15:47 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-04-03 10:58 [musl] graceful nscd fallback on kernels without AF_UNIX support Joakim Sindholt
2021-04-03 14:42 ` Rich Felker
2021-04-03 15:03   ` Joakim Sindholt
2021-04-03 15:47     ` Rich Felker

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