Re: semodule dumps core

From: Stephen Smalley <sds_at_tycho.nsa.gov>
Date: Mon, 20 Mar 2006 12:02:32 -0500

On Sat, 2006-03-18 at 01:02 +0100, Thomas Bleher wrote:
> * Thomas Bleher <bleher@informatik.uni-muenchen.de> [2006-03-16 23:56]:
> > Seems like semodule doesn't like me. I just recompiled my policy with
> > the new versions of the tools and now semodule dumps core when I do a
> > "semodule -b base.pp".
>
> Stephen gave me many good suggestions, among them to compile without
> -O2. I tried this and the problem went away! Tracking this down further
> I narrowed it down to libsepol being miscompiled with -O2, it works fine
> with -O0 or -O1. So this looks like a compiler bug in gcc (as shipped in
> current Ubuntu Dapper). Unfortunately I won't have time to track down
> this problem but if anyone wants to look into this I can provide the
> sources I used.

Ok, I reproduced this on Fedora by building libsepol with just -O2 by hand, e.g. make CFLAGS+="-O2" clean install. Looking at what an rpm build of the libsepol package does, it does build with -O2 but also adds several other flags during the build. Trying these flags individually with -O2, it appears that the -fstack-protector option makes the difference: adding it yields a working libsepol while removing it leaves a broken libsepol. As -fstack-protector adds guard variables and checking code, it seemed likely that it was covering up some bug that would otherwise occur. Looking at sepol_module_package_write() again, since the seg fault occurred immediately after it completed, I noticed that buf[] is too small if you include all optional sections (i.e. users_extra and seusers as well as file_contexts). Patch below.

Index: libsepol/src/module.c

---

RCS file: /nfshome/pal/CVS/selinux-usr/libsepol/src/module.c,v retrieving revision 1.19
diff -u -p -r1.19 module.c

--- libsepol/src/module.c	7 Feb 2006 14:04:43 -0000	1.19
+++ libsepol/src/module.c	20 Mar 2006 16:37:45 -0000

@@ -661,7 +661,7 @@ int sepol_module_package_write(sepol_mod  {

 	struct policy_file *file = &spf->pf;
 	policy_file_t polfile;
-	uint32_t buf[3], offsets[5], len, nsec = 0;
+	uint32_t buf[5], offsets[5], len, nsec = 0;
 	int i;
 
 	if (p->policy) {

-- 
Stephen Smalley
National Security Agency


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Received on Mon 20 Mar 2006 - 11:57:43 EST