bpf-fixes

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Merge tag 'bpf-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf

Pull bpf fixes from Alexei Starovoitov:

 - Fix use-after-free in libbpf when map is resized (Adin Scannell)

 - Fix verifier assumptions about 2nd argument of bpf_sysctl_get_name
   (Jerome Marchand)

 - Fix verifier assumption of nullness of d_inode in dentry (Song Liu)

 - Fix global starvation of LRU map (Willem de Bruijn)

 - Fix potential NULL dereference in btf_dump__free (Yuan Chen)

* tag 'bpf-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf:
  selftests/bpf: adapt one more case in test_lru_map to the new target_free
  libbpf: Fix possible use-after-free for externs
  selftests/bpf: Convert test_sysctl to prog_tests
  bpf: Specify access type of bpf_sysctl_get_name args
  libbpf: Fix null pointer dereference in btf_dump__free on allocation failure
  bpf: Adjust free target to avoid global starvation of LRU map
  bpf: Mark dentry->d_inode as trusted_or_null

Documentation/bpf/map_hash.rst

@@ -233,10 +233,16 @@ attempts in order to enforce the LRU property which have increasing impacts on
 other CPUs involved in the following operation attempts:
 
 - Attempt to use CPU-local state to batch operations
-- Attempt to fetch free nodes from global lists
+- Attempt to fetch ``target_free`` free nodes from global lists
 - Attempt to pull any node from a global list and remove it from the hashmap
 - Attempt to pull any node from any CPU's list and remove it from the hashmap
 
+The number of nodes to borrow from the global list in a batch, ``target_free``,
+depends on the size of the map. Larger batch size reduces lock contention, but
+may also exhaust the global structure. The value is computed at map init to
+avoid exhaustion, by limiting aggregate reservation by all CPUs to half the map
+size. With a minimum of a single element and maximum budget of 128 at a time.
+
 This algorithm is described visually in the following diagram. See the
 description in commit 3a08c2fd7634 ("bpf: LRU List") for a full explanation of
 the corresponding operations:

Documentation/bpf/map_lru_hash_update.dot

@@ -35,18 +35,18 @@ digraph {
   fn_bpf_lru_list_pop_free_to_local [shape=rectangle,fillcolor=2,
     label="Flush local pending,
     Rotate Global list, move
-    LOCAL_FREE_TARGET
+    target_free
     from global -> local"]
   // Also corresponds to:
   // fn__local_list_flush()
   // fn_bpf_lru_list_rotate()
   fn___bpf_lru_node_move_to_free[shape=diamond,fillcolor=2,
-    label="Able to free\nLOCAL_FREE_TARGET\nnodes?"]
+    label="Able to free\ntarget_free\nnodes?"]
 
   fn___bpf_lru_list_shrink_inactive [shape=rectangle,fillcolor=3,
     label="Shrink inactive list
       up to remaining
-      LOCAL_FREE_TARGET
+      target_free
       (global LRU -> local)"]
   fn___bpf_lru_list_shrink [shape=diamond,fillcolor=2,
     label="> 0 entries in\nlocal free list?"]

kernel/bpf/bpf_lru_list.c

@@ -337,12 +337,12 @@ static void bpf_lru_list_pop_free_to_local(struct bpf_lru *lru,
 				 list) {
 		__bpf_lru_node_move_to_free(l, node, local_free_list(loc_l),
 					    BPF_LRU_LOCAL_LIST_T_FREE);
-		if (++nfree == LOCAL_FREE_TARGET)
+		if (++nfree == lru->target_free)
 			break;
 	}
 
-	if (nfree < LOCAL_FREE_TARGET)
-		__bpf_lru_list_shrink(lru, l, LOCAL_FREE_TARGET - nfree,
+	if (nfree < lru->target_free)
+		__bpf_lru_list_shrink(lru, l, lru->target_free - nfree,
 				      local_free_list(loc_l),
 				      BPF_LRU_LOCAL_LIST_T_FREE);
 
@@ -577,6 +577,9 @@ static void bpf_common_lru_populate(struct bpf_lru *lru, void *buf,
 		list_add(&node->list, &l->lists[BPF_LRU_LIST_T_FREE]);
 		buf += elem_size;
 	}
+
+	lru->target_free = clamp((nr_elems / num_possible_cpus()) / 2,
+				 1, LOCAL_FREE_TARGET);
 }
 
 static void bpf_percpu_lru_populate(struct bpf_lru *lru, void *buf,

kernel/bpf/bpf_lru_list.h

@@ -58,6 +58,7 @@ struct bpf_lru {
 	del_from_htab_func del_from_htab;
 	void *del_arg;
 	unsigned int hash_offset;
+	unsigned int target_free;
 	unsigned int nr_scans;
 	bool percpu;
 };

kernel/bpf/cgroup.c

@@ -2134,7 +2134,7 @@ static const struct bpf_func_proto bpf_sysctl_get_name_proto = {
 	.gpl_only	= false,
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_PTR_TO_CTX,
-	.arg2_type	= ARG_PTR_TO_MEM,
+	.arg2_type	= ARG_PTR_TO_MEM | MEM_WRITE,
 	.arg3_type	= ARG_CONST_SIZE,
 	.arg4_type	= ARG_ANYTHING,
 };

kernel/bpf/verifier.c

@@ -7027,8 +7027,7 @@ BTF_TYPE_SAFE_TRUSTED(struct file) {
 	struct inode *f_inode;
 };
 
-BTF_TYPE_SAFE_TRUSTED(struct dentry) {
-	/* no negative dentry-s in places where bpf can see it */
+BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct dentry) {
 	struct inode *d_inode;
 };
 
@@ -7066,7 +7065,6 @@ static bool type_is_trusted(struct bpf_verifier_env *env,
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED(struct bpf_iter__task));
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED(struct linux_binprm));
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED(struct file));
-	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED(struct dentry));
 
 	return btf_nested_type_is_trusted(&env->log, reg, field_name, btf_id, "__safe_trusted");
 }
@@ -7076,6 +7074,7 @@ static bool type_is_trusted_or_null(struct bpf_verifier_env *env,
 				    const char *field_name, u32 btf_id)
 {
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct socket));
+	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct dentry));
 
 	return btf_nested_type_is_trusted(&env->log, reg, field_name, btf_id,
 					  "__safe_trusted_or_null");

tools/lib/bpf/btf_dump.c

@@ -226,6 +226,9 @@ static void btf_dump_free_names(struct hashmap *map)
 	size_t bkt;
 	struct hashmap_entry *cur;
 
+	if (!map)
+		return;
+
 	hashmap__for_each_entry(map, cur, bkt)
 		free((void *)cur->pkey);
 

tools/lib/bpf/libbpf.c

@@ -597,7 +597,7 @@ struct extern_desc {
 	int sym_idx;
 	int btf_id;
 	int sec_btf_id;
-	const char *name;
+	char *name;
 	char *essent_name;
 	bool is_set;
 	bool is_weak;
@@ -4259,7 +4259,9 @@ static int bpf_object__collect_externs(struct bpf_object *obj)
 			return ext->btf_id;
 		}
 		t = btf__type_by_id(obj->btf, ext->btf_id);
-		ext->name = btf__name_by_offset(obj->btf, t->name_off);
+		ext->name = strdup(btf__name_by_offset(obj->btf, t->name_off));
+		if (!ext->name)
+			return -ENOMEM;
 		ext->sym_idx = i;
 		ext->is_weak = ELF64_ST_BIND(sym->st_info) == STB_WEAK;
 
@@ -9138,8 +9140,10 @@ void bpf_object__close(struct bpf_object *obj)
 	zfree(&obj->btf_custom_path);
 	zfree(&obj->kconfig);
 
-	for (i = 0; i < obj->nr_extern; i++)
+	for (i = 0; i < obj->nr_extern; i++) {
+		zfree(&obj->externs[i].name);
 		zfree(&obj->externs[i].essent_name);
+	}
 
 	zfree(&obj->externs);
 	obj->nr_extern = 0;

tools/testing/selftests/bpf/.gitignore

@@ -21,7 +21,6 @@ test_lirc_mode2_user
 flow_dissector_load
 test_tcpnotify_user
 test_libbpf
-test_sysctl
 xdping
 test_cpp
 *.d

tools/testing/selftests/bpf/Makefile

@@ -73,7 +73,7 @@ endif
 # Order correspond to 'make run_tests' order
 TEST_GEN_PROGS = test_verifier test_tag test_maps test_lru_map test_progs \
 	test_sockmap \
-	test_tcpnotify_user test_sysctl \
+	test_tcpnotify_user \
 	test_progs-no_alu32
 TEST_INST_SUBDIRS := no_alu32
 
@@ -220,7 +220,7 @@ ifeq ($(VMLINUX_BTF),)
 $(error Cannot find a vmlinux for VMLINUX_BTF at any of "$(VMLINUX_BTF_PATHS)")
 endif
 
-# Define simple and short `make test_progs`, `make test_sysctl`, etc targets
+# Define simple and short `make test_progs`, `make test_maps`, etc targets
 # to build individual tests.
 # NOTE: Semicolon at the end is critical to override lib.mk's default static
 # rule for binaries.
@@ -329,7 +329,6 @@ NETWORK_HELPERS := $(OUTPUT)/network_helpers.o
 $(OUTPUT)/test_sockmap: $(CGROUP_HELPERS) $(TESTING_HELPERS)
 $(OUTPUT)/test_tcpnotify_user: $(CGROUP_HELPERS) $(TESTING_HELPERS) $(TRACE_HELPERS)
 $(OUTPUT)/test_sock_fields: $(CGROUP_HELPERS) $(TESTING_HELPERS)
-$(OUTPUT)/test_sysctl: $(CGROUP_HELPERS) $(TESTING_HELPERS)
 $(OUTPUT)/test_tag: $(TESTING_HELPERS)
 $(OUTPUT)/test_lirc_mode2_user: $(TESTING_HELPERS)
 $(OUTPUT)/xdping: $(TESTING_HELPERS)

tools/testing/selftests/bpf/prog_tests/test_sysctl.c

@@ -1,22 +1,8 @@
 // SPDX-License-Identifier: GPL-2.0
 // Copyright (c) 2019 Facebook
 
-#include <fcntl.h>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
-
-#include <linux/filter.h>
-
-#include <bpf/bpf.h>
-#include <bpf/libbpf.h>
-
-#include <bpf/bpf_endian.h>
-#include "bpf_util.h"
+#include "test_progs.h"
 #include "cgroup_helpers.h"
-#include "testing_helpers.h"
 
 #define CG_PATH			"/foo"
 #define MAX_INSNS		512
@@ -1608,26 +1594,19 @@ static int run_tests(int cgfd)
 	return fails ? -1 : 0;
 }
 
-int main(int argc, char **argv)
+void test_sysctl(void)
 {
-	int cgfd = -1;
-	int err = 0;
+	int cgfd;
 
 	cgfd = cgroup_setup_and_join(CG_PATH);
-	if (cgfd < 0)
-		goto err;
+	if (!ASSERT_OK_FD(cgfd < 0, "create_cgroup"))
+		goto out;
 
-	/* Use libbpf 1.0 API mode */
-	libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
+	if (!ASSERT_OK(run_tests(cgfd), "run_tests"))
+		goto out;
 
-	if (run_tests(cgfd))
-		goto err;
-
-	goto out;
-err:
-	err = -1;
 out:
 	close(cgfd);
 	cleanup_cgroup_environment();
-	return err;
+	return;
 }

tools/testing/selftests/bpf/progs/test_global_map_resize.c

@@ -32,6 +32,16 @@ int my_int_last SEC(".data.array_not_last");
 
 int percpu_arr[1] SEC(".data.percpu_arr");
 
+/* at least one extern is included, to ensure that a specific
+ * regression is tested whereby resizing resulted in a free-after-use
+ * bug after type information is invalidated by the resize operation.
+ *
+ * There isn't a particularly good API to test for this specific condition,
+ * but by having externs for the resizing tests it will cover this path.
+ */
+extern int LINUX_KERNEL_VERSION __kconfig;
+long version_sink;
+
 SEC("tp/syscalls/sys_enter_getpid")
 int bss_array_sum(void *ctx)
 {
@@ -44,6 +54,9 @@ int bss_array_sum(void *ctx)
 	for (size_t i = 0; i < bss_array_len; ++i)
 		sum += array[i];
 
+	/* see above; ensure this is not optimized out */
+	version_sink = LINUX_KERNEL_VERSION;
+
 	return 0;
 }
 
@@ -59,6 +72,9 @@ int data_array_sum(void *ctx)
 	for (size_t i = 0; i < data_array_len; ++i)
 		sum += my_array[i];
 
+	/* see above; ensure this is not optimized out */
+	version_sink = LINUX_KERNEL_VERSION;
+
 	return 0;
 }
 

tools/testing/selftests/bpf/progs/verifier_vfs_accept.c

@@ -2,6 +2,7 @@
 /* Copyright (c) 2024 Google LLC. */
 
 #include <vmlinux.h>
+#include <errno.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
@@ -82,4 +83,21 @@ int BPF_PROG(path_d_path_from_file_argument, struct file *file)
 	return 0;
 }
 
+SEC("lsm.s/inode_rename")
+__success
+int BPF_PROG(inode_rename, struct inode *old_dir, struct dentry *old_dentry,
+	     struct inode *new_dir, struct dentry *new_dentry,
+	     unsigned int flags)
+{
+	struct inode *inode = new_dentry->d_inode;
+	ino_t ino;
+
+	if (!inode)
+		return 0;
+	ino = inode->i_ino;
+	if (ino == 0)
+		return -EACCES;
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/progs/verifier_vfs_reject.c

@@ -2,6 +2,7 @@
 /* Copyright (c) 2024 Google LLC. */
 
 #include <vmlinux.h>
+#include <errno.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 #include <linux/limits.h>
@@ -158,4 +159,18 @@ int BPF_PROG(path_d_path_kfunc_non_lsm, struct path *path, struct file *f)
 	return 0;
 }
 
+SEC("lsm.s/inode_rename")
+__failure __msg("invalid mem access 'trusted_ptr_or_null_'")
+int BPF_PROG(inode_rename, struct inode *old_dir, struct dentry *old_dentry,
+	     struct inode *new_dir, struct dentry *new_dentry,
+	     unsigned int flags)
+{
+	struct inode *inode = new_dentry->d_inode;
+	ino_t ino;
+
+	ino = inode->i_ino;
+	if (ino == 0)
+		return -EACCES;
+	return 0;
+}
 char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/test_lru_map.c

@@ -138,6 +138,18 @@ static int sched_next_online(int pid, int *next_to_try)
 	return ret;
 }
 
+/* Derive target_free from map_size, same as bpf_common_lru_populate */
+static unsigned int __tgt_size(unsigned int map_size)
+{
+	return (map_size / nr_cpus) / 2;
+}
+
+/* Inverse of how bpf_common_lru_populate derives target_free from map_size. */
+static unsigned int __map_size(unsigned int tgt_free)
+{
+	return tgt_free * nr_cpus * 2;
+}
+
 /* Size of the LRU map is 2
  * Add key=1 (+1 key)
  * Add key=2 (+1 key)
@@ -231,11 +243,11 @@ static void test_lru_sanity0(int map_type, int map_flags)
 	printf("Pass\n");
 }
 
-/* Size of the LRU map is 1.5*tgt_free
- * Insert 1 to tgt_free (+tgt_free keys)
- * Lookup 1 to tgt_free/2
- * Insert 1+tgt_free to 2*tgt_free (+tgt_free keys)
- * => 1+tgt_free/2 to LOCALFREE_TARGET will be removed by LRU
+/* Verify that unreferenced elements are recycled before referenced ones.
+ * Insert elements.
+ * Reference a subset of these.
+ * Insert more, enough to trigger recycling.
+ * Verify that unreferenced are recycled.
  */
 static void test_lru_sanity1(int map_type, int map_flags, unsigned int tgt_free)
 {
@@ -257,7 +269,7 @@ static void test_lru_sanity1(int map_type, int map_flags, unsigned int tgt_free)
 	batch_size = tgt_free / 2;
 	assert(batch_size * 2 == tgt_free);
 
-	map_size = tgt_free + batch_size;
+	map_size = __map_size(tgt_free) + batch_size;
 	lru_map_fd = create_map(map_type, map_flags, map_size);
 	assert(lru_map_fd != -1);
 
@@ -266,13 +278,13 @@ static void test_lru_sanity1(int map_type, int map_flags, unsigned int tgt_free)
 
 	value[0] = 1234;
 
-	/* Insert 1 to tgt_free (+tgt_free keys) */
-	end_key = 1 + tgt_free;
+	/* Insert map_size - batch_size keys */
+	end_key = 1 + __map_size(tgt_free);
 	for (key = 1; key < end_key; key++)
 		assert(!bpf_map_update_elem(lru_map_fd, &key, value,
 					    BPF_NOEXIST));
 
-	/* Lookup 1 to tgt_free/2 */
+	/* Lookup 1 to batch_size */
 	end_key = 1 + batch_size;
 	for (key = 1; key < end_key; key++) {
 		assert(!bpf_map_lookup_elem_with_ref_bit(lru_map_fd, key, value));
@@ -280,12 +292,13 @@ static void test_lru_sanity1(int map_type, int map_flags, unsigned int tgt_free)
 					    BPF_NOEXIST));
 	}
 
-	/* Insert 1+tgt_free to 2*tgt_free
-	 * => 1+tgt_free/2 to LOCALFREE_TARGET will be
+	/* Insert another map_size - batch_size keys
+	 * Map will contain 1 to batch_size plus these latest, i.e.,
+	 * => previous 1+batch_size to map_size - batch_size will have been
 	 * removed by LRU
 	 */
-	key = 1 + tgt_free;
-	end_key = key + tgt_free;
+	key = 1 + __map_size(tgt_free);
+	end_key = key + __map_size(tgt_free);
 	for (; key < end_key; key++) {
 		assert(!bpf_map_update_elem(lru_map_fd, &key, value,
 					    BPF_NOEXIST));
@@ -301,17 +314,8 @@ static void test_lru_sanity1(int map_type, int map_flags, unsigned int tgt_free)
 	printf("Pass\n");
 }
 
-/* Size of the LRU map 1.5 * tgt_free
- * Insert 1 to tgt_free (+tgt_free keys)
- * Update 1 to tgt_free/2
- *   => The original 1 to tgt_free/2 will be removed due to
- *      the LRU shrink process
- * Re-insert 1 to tgt_free/2 again and do a lookup immeidately
- * Insert 1+tgt_free to tgt_free*3/2
- * Insert 1+tgt_free*3/2 to tgt_free*5/2
- *   => Key 1+tgt_free to tgt_free*3/2
- *      will be removed from LRU because it has never
- *      been lookup and ref bit is not set
+/* Verify that insertions exceeding map size will recycle the oldest.
+ * Verify that unreferenced elements are recycled before referenced.
  */
 static void test_lru_sanity2(int map_type, int map_flags, unsigned int tgt_free)
 {
@@ -334,7 +338,7 @@ static void test_lru_sanity2(int map_type, int map_flags, unsigned int tgt_free)
 	batch_size = tgt_free / 2;
 	assert(batch_size * 2 == tgt_free);
 
-	map_size = tgt_free + batch_size;
+	map_size = __map_size(tgt_free) + batch_size;
 	lru_map_fd = create_map(map_type, map_flags, map_size);
 	assert(lru_map_fd != -1);
 
@@ -343,8 +347,8 @@ static void test_lru_sanity2(int map_type, int map_flags, unsigned int tgt_free)
 
 	value[0] = 1234;
 
-	/* Insert 1 to tgt_free (+tgt_free keys) */
-	end_key = 1 + tgt_free;
+	/* Insert map_size - batch_size keys */
+	end_key = 1 + __map_size(tgt_free);
 	for (key = 1; key < end_key; key++)
 		assert(!bpf_map_update_elem(lru_map_fd, &key, value,
 					    BPF_NOEXIST));
@@ -357,8 +361,7 @@ static void test_lru_sanity2(int map_type, int map_flags, unsigned int tgt_free)
 	 * shrink the inactive list to get tgt_free
 	 * number of free nodes.
 	 *
-	 * Hence, the oldest key 1 to tgt_free/2
-	 * are removed from the LRU list.
+	 * Hence, the oldest key is removed from the LRU list.
 	 */
 	key = 1;
 	if (map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) {
@@ -370,8 +373,7 @@ static void test_lru_sanity2(int map_type, int map_flags, unsigned int tgt_free)
 					   BPF_EXIST));
 	}
 
-	/* Re-insert 1 to tgt_free/2 again and do a lookup
-	 * immeidately.
+	/* Re-insert 1 to batch_size again and do a lookup immediately.
 	 */
 	end_key = 1 + batch_size;
 	value[0] = 4321;
@@ -387,17 +389,18 @@ static void test_lru_sanity2(int map_type, int map_flags, unsigned int tgt_free)
 
 	value[0] = 1234;
 
-	/* Insert 1+tgt_free to tgt_free*3/2 */
-	end_key = 1 + tgt_free + batch_size;
-	for (key = 1 + tgt_free; key < end_key; key++)
+	/* Insert batch_size new elements */
+	key = 1 + __map_size(tgt_free);
+	end_key = key + batch_size;
+	for (; key < end_key; key++)
 		/* These newly added but not referenced keys will be
 		 * gone during the next LRU shrink.
 		 */
 		assert(!bpf_map_update_elem(lru_map_fd, &key, value,
 					    BPF_NOEXIST));
 
-	/* Insert 1+tgt_free*3/2 to  tgt_free*5/2 */
-	end_key = key + tgt_free;
+	/* Insert map_size - batch_size elements */
+	end_key += __map_size(tgt_free);
 	for (; key < end_key; key++) {
 		assert(!bpf_map_update_elem(lru_map_fd, &key, value,
 					    BPF_NOEXIST));
@@ -413,12 +416,12 @@ static void test_lru_sanity2(int map_type, int map_flags, unsigned int tgt_free)
 	printf("Pass\n");
 }
 
-/* Size of the LRU map is 2*tgt_free
- * It is to test the active/inactive list rotation
- * Insert 1 to 2*tgt_free (+2*tgt_free keys)
- * Lookup key 1 to tgt_free*3/2
- * Add 1+2*tgt_free to tgt_free*5/2 (+tgt_free/2 keys)
- *  => key 1+tgt_free*3/2 to 2*tgt_free are removed from LRU
+/* Test the active/inactive list rotation
+ *
+ * Fill the whole map, deplete the free list.
+ * Reference all except the last lru->target_free elements.
+ * Insert lru->target_free new elements. This triggers one shrink.
+ * Verify that the non-referenced elements are replaced.
  */
 static void test_lru_sanity3(int map_type, int map_flags, unsigned int tgt_free)
 {
@@ -437,8 +440,7 @@ static void test_lru_sanity3(int map_type, int map_flags, unsigned int tgt_free)
 
 	assert(sched_next_online(0, &next_cpu) != -1);
 
-	batch_size = tgt_free / 2;
-	assert(batch_size * 2 == tgt_free);
+	batch_size = __tgt_size(tgt_free);
 
 	map_size = tgt_free * 2;
 	lru_map_fd = create_map(map_type, map_flags, map_size);
@@ -449,23 +451,21 @@ static void test_lru_sanity3(int map_type, int map_flags, unsigned int tgt_free)
 
 	value[0] = 1234;
 
-	/* Insert 1 to 2*tgt_free (+2*tgt_free keys) */
-	end_key = 1 + (2 * tgt_free);
+	/* Fill the map */
+	end_key = 1 + map_size;
 	for (key = 1; key < end_key; key++)
 		assert(!bpf_map_update_elem(lru_map_fd, &key, value,
 					    BPF_NOEXIST));
 
-	/* Lookup key 1 to tgt_free*3/2 */
-	end_key = tgt_free + batch_size;
+	/* Reference all but the last batch_size */
+	end_key = 1 + map_size - batch_size;
 	for (key = 1; key < end_key; key++) {
 		assert(!bpf_map_lookup_elem_with_ref_bit(lru_map_fd, key, value));
 		assert(!bpf_map_update_elem(expected_map_fd, &key, value,
 					    BPF_NOEXIST));
 	}
 
-	/* Add 1+2*tgt_free to tgt_free*5/2
-	 * (+tgt_free/2 keys)
-	 */
+	/* Insert new batch_size: replaces the non-referenced elements */
 	key = 2 * tgt_free + 1;
 	end_key = key + batch_size;
 	for (; key < end_key; key++) {
@@ -500,7 +500,8 @@ static void test_lru_sanity4(int map_type, int map_flags, unsigned int tgt_free)
 		lru_map_fd = create_map(map_type, map_flags,
 					3 * tgt_free * nr_cpus);
 	else
-		lru_map_fd = create_map(map_type, map_flags, 3 * tgt_free);
+		lru_map_fd = create_map(map_type, map_flags,
+					3 * __map_size(tgt_free));
 	assert(lru_map_fd != -1);
 
 	expected_map_fd = create_map(BPF_MAP_TYPE_HASH, 0,