Merge branch 'bpf-cpumap-improve-error-propagation-in-cpu_map_update_elem'

Kohei Enju says:

====================
bpf: cpumap: improve error propagation in cpu_map_update_elem()

This series improves error propagation in cpumap and adds selftests that
cover the failure cases.

Currently, failures returned from __cpu_map_entry_alloc() are ignored
and always converted to -ENOMEM by cpu_map_update_elem(). This series
ensures the correct error propagation and adds selftests.

Changes:
  v2:
    - send to bpf-next, not to bpf
    - drop Fixes: tag
  v1: https://lore.kernel.org/bpf/[email protected]/
====================

Link: https://patch.msgid.link/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: Alexei Starovoitov

kernel/bpf/cpumap.c

@@ -430,7 +430,7 @@ static struct bpf_cpu_map_entry *
 __cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value,
 		      u32 cpu)
 {
-	int numa, err, i, fd = value->bpf_prog.fd;
+	int numa, err = -ENOMEM, i, fd = value->bpf_prog.fd;
 	gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
 	struct bpf_cpu_map_entry *rcpu;
 	struct xdp_bulk_queue *bq;
@@ -440,7 +440,7 @@ __cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value,
 
 	rcpu = bpf_map_kmalloc_node(map, sizeof(*rcpu), gfp | __GFP_ZERO, numa);
 	if (!rcpu)
-		return NULL;
+		return ERR_PTR(err);
 
 	/* Alloc percpu bulkq */
 	rcpu->bulkq = bpf_map_alloc_percpu(map, sizeof(*rcpu->bulkq),
@@ -468,16 +468,21 @@ __cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value,
 	rcpu->value.qsize  = value->qsize;
 	gro_init(&rcpu->gro);
 
-	if (fd > 0 && __cpu_map_load_bpf_program(rcpu, map, fd))
-		goto free_ptr_ring;
+	if (fd > 0) {
+		err = __cpu_map_load_bpf_program(rcpu, map, fd);
+		if (err)
+			goto free_ptr_ring;
+	}
 
 	/* Setup kthread */
 	init_completion(&rcpu->kthread_running);
 	rcpu->kthread = kthread_create_on_node(cpu_map_kthread_run, rcpu, numa,
 					       "cpumap/%d/map:%d", cpu,
 					       map->id);
-	if (IS_ERR(rcpu->kthread))
+	if (IS_ERR(rcpu->kthread)) {
+		err = PTR_ERR(rcpu->kthread);
 		goto free_prog;
+	}
 
 	/* Make sure kthread runs on a single CPU */
 	kthread_bind(rcpu->kthread, cpu);
@@ -503,7 +508,7 @@ __cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value,
 	free_percpu(rcpu->bulkq);
 free_rcu:
 	kfree(rcpu);
-	return NULL;
+	return ERR_PTR(err);
 }
 
 static void __cpu_map_entry_free(struct work_struct *work)
@@ -596,8 +601,8 @@ static long cpu_map_update_elem(struct bpf_map *map, void *key, void *value,
 	} else {
 		/* Updating qsize cause re-allocation of bpf_cpu_map_entry */
 		rcpu = __cpu_map_entry_alloc(map, &cpumap_value, key_cpu);
-		if (!rcpu)
-			return -ENOMEM;
+		if (IS_ERR(rcpu))
+			return PTR_ERR(rcpu);
 	}
 	rcu_read_lock();
 	__cpu_map_entry_replace(cmap, key_cpu, rcpu);

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

@@ -18,7 +18,7 @@ static void test_xdp_with_cpumap_helpers(void)
 	struct bpf_cpumap_val val = {
 		.qsize = 192,
 	};
-	int err, prog_fd, prog_redir_fd, map_fd;
+	int err, prog_fd, prog_redir_fd, map_fd, bad_fd;
 	struct nstoken *nstoken = NULL;
 	__u32 idx = 0;
 
@@ -79,7 +79,22 @@ static void test_xdp_with_cpumap_helpers(void)
 	val.qsize = 192;
 	val.bpf_prog.fd = bpf_program__fd(skel->progs.xdp_dummy_prog);
 	err = bpf_map_update_elem(map_fd, &idx, &val, 0);
-	ASSERT_NEQ(err, 0, "Add non-BPF_XDP_CPUMAP program to cpumap entry");
+	ASSERT_EQ(err, -EINVAL, "Add non-BPF_XDP_CPUMAP program to cpumap entry");
+
+	/* Try to attach non-BPF file descriptor */
+	bad_fd = open("/dev/null", O_RDONLY);
+	ASSERT_GE(bad_fd, 0, "Open /dev/null for non-BPF fd");
+
+	val.bpf_prog.fd = bad_fd;
+	err = bpf_map_update_elem(map_fd, &idx, &val, 0);
+	ASSERT_EQ(err, -EINVAL, "Add non-BPF fd to cpumap entry");
+
+	/* Try to attach nonexistent file descriptor */
+	err = close(bad_fd);
+	ASSERT_EQ(err, 0, "Close non-BPF fd for nonexistent fd");
+
+	err = bpf_map_update_elem(map_fd, &idx, &val, 0);
+	ASSERT_EQ(err, -EBADF, "Add nonexistent fd to cpumap entry");
 
 	/* Try to attach BPF_XDP program with frags to cpumap when we have
 	 * already loaded a BPF_XDP program on the map