[RFC,05/22] selinux: avoid nontransitive comparison

Commit Message

Christian Göttsche Nov. 15, 2024, 1:35 p.m. UTC

From: Christian Göttsche <[e-mail]>

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 <[e-mail]>
---
 security/selinux/ss/policydb.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

Patch

diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
index 383f3ae82a73..d04d9ada3835 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] = {
@@ -421,11 +423,11 @@  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;
 
@@ -456,15 +458,15 @@  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;
 }
@@ -493,15 +495,15 @@  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 = {