livepatch/samples/selftest: Use klp_shadow_alloc() API correctly

The commit e91c2518a5d22a ("livepatch: Initialize shadow variables
safely by a custom callback") leads to the following static checker
warning:

samples/livepatch/livepatch-shadow-fix1.c:86 livepatch_fix1_dummy_alloc()
error: 'klp_shadow_alloc()' 'leak' too small (4 vs 8)

It is because klp_shadow_alloc() is used a wrong way:

int *leak;
shadow_leak = klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
shadow_leak_ctor, leak);

The code is supposed to store the "leak" pointer into the shadow variable.
3rd parameter correctly passes size of the data (size of pointer). But
the 5th parameter is wrong. It should pass pointer to the data (pointer
to the pointer) but it passes the pointer directly.

It works because shadow_leak_ctor() handle "ctor_data" as the data
instead of pointer to the data. But it is semantically wrong and
confusing.

The same problem is also in the module used by selftests. In this case,
"pvX" variables are introduced. They represent the data stored in
the shadow variables.

Reported-by: Dan Carpenter <[e-mail]>
Signed-off-by: Petr Mladek <[e-mail]>
Reviewed-by: Joe Lawrence <[e-mail]>
Acked-by: Miroslav Benes <[e-mail]>
Reviewed-by: Kamalesh Babulal <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>

lib/livepatch/test_klp_shadow_vars.c

···
 			  gfp_t gfp_flags, klp_shadow_ctor_t ctor,
 			  void *ctor_data)
 {
-	int *var = ctor_data;
+	int **var = ctor_data;
 	int **sv;
 
 	sv = klp_shadow_alloc(obj, id, size, gfp_flags, ctor, var);
 	pr_info("klp_%s(obj=PTR%d, id=0x%lx, size=%zx, gfp_flags=%pGg), ctor=PTR%d, ctor_data=PTR%d = PTR%d\n",
 		__func__, ptr_id(obj), id, size, &gfp_flags, ptr_id(ctor),
-		ptr_id(var), ptr_id(sv));
+		ptr_id(*var), ptr_id(sv));
 
 	return sv;
 }
···
 				 gfp_t gfp_flags, klp_shadow_ctor_t ctor,
 				 void *ctor_data)
 {
-	int *var = ctor_data;
+	int **var = ctor_data;
 	int **sv;
 
 	sv = klp_shadow_get_or_alloc(obj, id, size, gfp_flags, ctor, var);
 	pr_info("klp_%s(obj=PTR%d, id=0x%lx, size=%zx, gfp_flags=%pGg), ctor=PTR%d, ctor_data=PTR%d = PTR%d\n",
 		__func__, ptr_id(obj), id, size, &gfp_flags, ptr_id(ctor),
-		ptr_id(var), ptr_id(sv));
+		ptr_id(*var), ptr_id(sv));
 
 	return sv;
 }
···
 static int shadow_ctor(void *obj, void *shadow_data, void *ctor_data)
 {
 	int **sv = shadow_data;
-	int *var = ctor_data;
+	int **var = ctor_data;
 
-	*sv = var;
+	if (!var)
+		return -EINVAL;
+
+	*sv = *var;
 	pr_info("%s: PTR%d -> PTR%d\n",
-		__func__, ptr_id(sv), ptr_id(var));
+		__func__, ptr_id(sv), ptr_id(*var));
 
 	return 0;
 }
···
 {
 	void *obj			= THIS_MODULE;
 	int id			= 0x1234;
-	size_t size		= sizeof(int *);
 	gfp_t gfp_flags		= GFP_KERNEL;
 
 	int var1, var2, var3, var4;
+	int *pv1, *pv2, *pv3, *pv4;
 	int **sv1, **sv2, **sv3, **sv4;
 
 	int **sv;
 
+	pv1 = &var1;
+	pv2 = &var2;
+	pv3 = &var3;
+	pv4 = &var4;
+
 	ptr_id(NULL);
-	ptr_id(&var1);
-	ptr_id(&var2);
-	ptr_id(&var3);
-	ptr_id(&var4);
+	ptr_id(pv1);
+	ptr_id(pv2);
+	ptr_id(pv3);
+	ptr_id(pv4);
 
 	/*
 	 * With an empty shadow variable hash table, expect not to find
···
 	/*
 	 * Allocate a few shadow variables with different <obj> and <id>.
 	 */
-	sv1 = shadow_alloc(obj, id, size, gfp_flags, shadow_ctor, &var1);
+	sv1 = shadow_alloc(obj, id, sizeof(pv1), gfp_flags, shadow_ctor, &pv1);
 	if (!sv1)
 		return -ENOMEM;
 
-	sv2 = shadow_alloc(obj + 1, id, size, gfp_flags, shadow_ctor, &var2);
+	sv2 = shadow_alloc(obj + 1, id, sizeof(pv2), gfp_flags, shadow_ctor, &pv2);
 	if (!sv2)
 		return -ENOMEM;
 
-	sv3 = shadow_alloc(obj, id + 1, size, gfp_flags, shadow_ctor, &var3);
+	sv3 = shadow_alloc(obj, id + 1, sizeof(pv3), gfp_flags, shadow_ctor, &pv3);
 	if (!sv3)
 		return -ENOMEM;
 
···
 	sv = shadow_get(obj, id);
 	if (!sv)
 		return -EINVAL;
-	if (sv == sv1 && *sv1 == &var1)
+	if (sv == sv1 && *sv1 == pv1)
 		pr_info("  got expected PTR%d -> PTR%d result\n",
 			ptr_id(sv1), ptr_id(*sv1));
 
 	sv = shadow_get(obj + 1, id);
 	if (!sv)
 		return -EINVAL;
-	if (sv == sv2 && *sv2 == &var2)
+	if (sv == sv2 && *sv2 == pv2)
 		pr_info("  got expected PTR%d -> PTR%d result\n",
 			ptr_id(sv2), ptr_id(*sv2));
 	sv = shadow_get(obj, id + 1);
 	if (!sv)
 		return -EINVAL;
-	if (sv == sv3 && *sv3 == &var3)
+	if (sv == sv3 && *sv3 == pv3)
 		pr_info("  got expected PTR%d -> PTR%d result\n",
 			ptr_id(sv3), ptr_id(*sv3));
 
···
 	 * Allocate or get a few more, this time with the same <obj>, <id>.
 	 * The second invocation should return the same shadow var.
 	 */
-	sv4 = shadow_get_or_alloc(obj + 2, id, size, gfp_flags, shadow_ctor, &var4);
+	sv4 = shadow_get_or_alloc(obj + 2, id, sizeof(pv4), gfp_flags, shadow_ctor, &pv4);
 	if (!sv4)
 		return -ENOMEM;
 
-	sv = shadow_get_or_alloc(obj + 2, id, size, gfp_flags, shadow_ctor, &var4);
+	sv = shadow_get_or_alloc(obj + 2, id, sizeof(pv4), gfp_flags, shadow_ctor, &pv4);
 	if (!sv)
 		return -EINVAL;
-	if (sv == sv4 && *sv4 == &var4)
+	if (sv == sv4 && *sv4 == pv4)
 		pr_info("  got expected PTR%d -> PTR%d result\n",
 			ptr_id(sv4), ptr_id(*sv4));
 
···
 	sv = shadow_get(obj, id + 1);
 	if (!sv)
 		return -EINVAL;
-	if (sv == sv3 && *sv3 == &var3)
+	if (sv == sv3 && *sv3 == pv3)
 		pr_info("  got expected PTR%d -> PTR%d result\n",
 			ptr_id(sv3), ptr_id(*sv3));
 

samples/livepatch/livepatch-shadow-fix1.c

···
 static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
 {
 	int **shadow_leak = shadow_data;
-	int *leak = ctor_data;
+	int **leak = ctor_data;
 
-	*shadow_leak = leak;
+	if (!ctor_data)
+		return -EINVAL;
+
+	*shadow_leak = *leak;
 	return 0;
 }
 
···
 	}
 
 	klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
-			 shadow_leak_ctor, leak);
+			 shadow_leak_ctor, &leak);
 
 	pr_info("%s: dummy @ %p, expires @ %lx\n",
 		__func__, d, d->jiffies_expire);