linux-kernel - [RFC PATCH v2 05/22] selinux: avoid nontransitive comparison

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Message-ID: <20241216164055.96267-5-cgoettsche@seltendoof.de>
Date: Mon, 16 Dec 2024 17:40:03 +0100
From: Christian Göttsche <cgoettsche@...tendoof.de>
To: selinux@...r.kernel.org
Cc: Christian Göttsche <cgzones@...glemail.com>,
	Paul Moore <paul@...l-moore.com>,
	Stephen Smalley <stephen.smalley.work@...il.com>,
	Ondrej Mosnacek <omosnace@...hat.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Thiébaud Weksteen <tweek@...gle.com>,
	Bram Bonné <brambonne@...gle.com>,
	Masahiro Yamada <masahiroy@...nel.org>,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: [RFC PATCH v2 05/22] selinux: avoid nontransitive comparison

From: Christian Göttsche <cgzones@...glemail.com>

Avoid using nontransitive comparison to prevent unexpected sorting
results due to (well-defined) overflows.
See https://www.qualys.com/2024/01/30/qsort.txt for a related issue in
glibc's qsort(3).

Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
---
 security/selinux/ss/policydb.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
index 3ba5506a3fff..eb944582d7a6 100644
--- a/security/selinux/ss/policydb.c
+++ b/security/selinux/ss/policydb.c
@@ -37,6 +37,8 @@
 #include "mls.h"
 #include "services.h"
 
+#define spaceship_cmp(a, b) (((a) > (b)) - ((a) < (b)))
+
 #ifdef CONFIG_SECURITY_SELINUX_DEBUG
 /* clang-format off */
 static const char *const symtab_name[SYM_NUM] = {
@@ -426,11 +428,11 @@ static int filenametr_cmp(const void *k1, const void *k2)
 	const struct filename_trans_key *ft2 = k2;
 	int v;
 
-	v = ft1->ttype - ft2->ttype;
+	v = spaceship_cmp(ft1->ttype, ft2->ttype);
 	if (v)
 		return v;
 
-	v = ft1->tclass - ft2->tclass;
+	v = spaceship_cmp(ft1->tclass, ft2->tclass);
 	if (v)
 		return v;
 
@@ -461,15 +463,15 @@ static int rangetr_cmp(const void *k1, const void *k2)
 	const struct range_trans *key1 = k1, *key2 = k2;
 	int v;
 
-	v = key1->source_type - key2->source_type;
+	v = spaceship_cmp(key1->source_type, key2->source_type);
 	if (v)
 		return v;
 
-	v = key1->target_type - key2->target_type;
+	v = spaceship_cmp(key1->target_type, key2->target_type);
 	if (v)
 		return v;
 
-	v = key1->target_class - key2->target_class;
+	v = spaceship_cmp(key1->target_class, key2->target_class);
 
 	return v;
 }
@@ -498,15 +500,15 @@ static int role_trans_cmp(const void *k1, const void *k2)
 	const struct role_trans_key *key1 = k1, *key2 = k2;
 	int v;
 
-	v = key1->role - key2->role;
+	v = spaceship_cmp(key1->role, key2->role);
 	if (v)
 		return v;
 
-	v = key1->type - key2->type;
+	v = spaceship_cmp(key1->type, key2->type);
 	if (v)
 		return v;
 
-	return key1->tclass - key2->tclass;
+	return spaceship_cmp(key1->tclass, key2->tclass);
 }
 
 static const struct hashtab_key_params roletr_key_params = {
-- 
2.45.2