code review 6455050: runtime: ignore signal 33 == SIGSETXID on GNU/Linux

runtime: ignore signal 33 == SIGSETXID on GNU/Linux

When a cgo program calls setuid, setgid, etc., the GNU/Linux
pthread library sends signal SIGSETXID to each thread to tell
it to update its UID info.  If Go is permitted to intercept
the default SIGSETXID signal handler, the program will hang.

This patch tells the runtime package to not try to intercept
SIGSETXID on GNU/Linux.  This will be odd if a Go program
wants to try to use that signal, but it means that cgo
programs that call setuid, etc., won't hang.

Fixes issue 3871.

[iant, 2012-07-27 04:28:22]

Hello rsc (cc: golang-dev@googlegroups.com),

I'd like you to review this change to
https://go.googlecode.com/hg/

[r, 2012-07-27 04:30:19]

s/intecept/intercept/ in the CL. otherwise LGTM but i am no expert.

-rob

[rsc, 2012-07-27 04:57:25]

LGTM

[minux1, 2012-07-27 05:19:48]

do you consider adding a test to /misc/cgo/test?

[bradfitzgoog, 2012-07-27 05:20:46]

Wouldn't it only work if the tests ran as root? Seems rare.
On Jul 26, 2012 10:19 PM, <minux.ma@gmail.com> wrote:

> do you consider adding a test to /misc/cgo/test?
>
>
http://codereview.appspot.com/**6455050/<http://codereview.appspot.com/6455050/>
>

[iant, 2012-07-27 05:46:31]

*** Submitted as http://code.google.com/p/go/source/detail?r=bfa4e1f1027f ***

runtime: ignore signal 33 == SIGSETXID on GNU/Linux

When a cgo program calls setuid, setgid, etc., the GNU/Linux
pthread library sends signal SIGSETXID to each thread to tell
it to update its UID info.  If Go is permitted to intercept
the default SIGSETXID signal handler, the program will hang.

This patch tells the runtime package to not try to intercept
SIGSETXID on GNU/Linux.  This will be odd if a Go program
wants to try to use that signal, but it means that cgo
programs that call setuid, etc., won't hang.

Fixes issue 3871.

R=rsc, r, minux.ma, bradfitz
CC=golang-dev
http://codereview.appspot.com/6455050

[iant2, 2012-07-27 05:51:09]

On Thu, Jul 26, 2012 at 10:19 PM,  <minux.ma@gmail.com> wrote:
> do you consider adding a test to /misc/cgo/test?

http://codereview.appspot.com/6445049

On Thu, Jul 26, 2012 at 10:20 PM, Brad Fitzpatrick <bradfitz@google.com> wrote:
> Wouldn't it only work if the tests ran as root? Seems rare.

The bug occurs even when non-root.  It's true that the call to setgid
fails, but it still tries to get every thread to fail individually.

Ian