From c1ef3b8e28777f70086c8d2ee851e3a0b5b4ca4c Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <tridge@samba.org>
Date: Sun, 24 Aug 2008 13:56:59 +1000
Subject: [PATCH] Avoid a race condition in glibc between AIO and setresuid().

See this test: http://samba.org/~tridge/junkcode/aio_uid.c

The problem is that setresuid() tries to be clever about threads, and
tries to change the euid of any threads that are running. If a AIO read
or write completes while this is going on then the signal from the thread
where the IO completed is lost, as it gets -1/EPERM from rt_sigqueueinfo()

The simplest fix is to try to use setreuid() instead of setresuid(),
as setreuid() doesn't try to be clever. Unfortunately this also means
we must use become_root()/unbecome_root() in the aio code.
(cherry picked from commit 5e3b978c51e741d413b856adafa1b1090ed8dd7b)
---
 source/configure.in | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/source/configure.in b/source/configure.in
index 7f8a97f99a5..dcdad47c3fd 100644
--- a/source/configure.in
+++ b/source/configure.in
@@ -2869,30 +2869,32 @@ fi
 ################################################
 # look for a method of setting the effective uid
 seteuid=no;
+
 if test $seteuid = no; then
-AC_CACHE_CHECK([for setresuid],samba_cv_USE_SETRESUID,[
+AC_CACHE_CHECK([for setreuid],samba_cv_USE_SETREUID,[
 AC_TRY_RUN([
 #define AUTOCONF_TEST 1
-#define USE_SETRESUID 1
+#define USE_SETREUID 1
 #include "confdefs.h"
 #include "${srcdir-.}/lib/util_sec.c"],
-           samba_cv_USE_SETRESUID=yes,samba_cv_USE_SETRESUID=no,samba_cv_USE_SETRESUID=cross)])
-if test x"$samba_cv_USE_SETRESUID" = x"yes"; then
-    seteuid=yes;AC_DEFINE(USE_SETRESUID,1,[Whether setresuid() is available])
+           samba_cv_USE_SETREUID=yes,samba_cv_USE_SETREUID=no,samba_cv_USE_SETREUID=cross)])
+if test x"$samba_cv_USE_SETREUID" = x"yes"; then
+    seteuid=yes;AC_DEFINE(USE_SETREUID,1,[Whether setreuid() is available])
 fi
 fi
 
-
+# we check for setresuid second as it conflicts with AIO on Linux. 
+# see http://samba.org/~tridge/junkcode/aio_uid.c
 if test $seteuid = no; then
-AC_CACHE_CHECK([for setreuid],samba_cv_USE_SETREUID,[
+AC_CACHE_CHECK([for setresuid],samba_cv_USE_SETRESUID,[
 AC_TRY_RUN([
 #define AUTOCONF_TEST 1
-#define USE_SETREUID 1
+#define USE_SETRESUID 1
 #include "confdefs.h"
 #include "${srcdir-.}/lib/util_sec.c"],
-           samba_cv_USE_SETREUID=yes,samba_cv_USE_SETREUID=no,samba_cv_USE_SETREUID=cross)])
-if test x"$samba_cv_USE_SETREUID" = x"yes"; then
-    seteuid=yes;AC_DEFINE(USE_SETREUID,1,[Whether setreuid() is available])
+           samba_cv_USE_SETRESUID=yes,samba_cv_USE_SETRESUID=no,samba_cv_USE_SETRESUID=cross)])
+if test x"$samba_cv_USE_SETRESUID" = x"yes"; then
+    seteuid=yes;AC_DEFINE(USE_SETRESUID,1,[Whether setresuid() is available])
 fi
 fi
 
-- 
2.34.1