From: Andrew Tridgell <tridge@samba.org>
Date: Sun, 24 Aug 2008 03:56:59 +0000 (+1000)
Subject: Avoid a race condition in glibc between AIO and setresuid().
X-Git-Tag: samba-4.0.0alpha6~801^2~202^2~8
X-Git-Url: http://git.samba.org/?p=samba.git;a=commitdiff_plain;h=d9f61dbdc91fae6560361f98d981b1f7bea80422;hp=52c39dd55d0a3eda3e9ed9a0981f546ca7b88cff

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.
(This used to be commit 56c5a6f024875bb79b0104beb36f6b0ec1e1e9f9)
---

diff --git a/source3/configure.in b/source3/configure.in
index 5508d9b01d5..9436fed1fff 100644
--- a/source3/configure.in
+++ b/source3/configure.in
@@ -2627,30 +2627,32 @@ AC_CHECK_FUNCS(getpagesize)
 ################################################
 # 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