[PATCH bpf-next v2 0/2] bpf: cpumap: improve error propagation in cpu_map_update_elem()

[PATCH bpf-next v2 0/2] bpf: cpumap: improve error propagation in cpu_map_update_elem()

[Kohei Enju]

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/20251128160504.57844-1-enjuk@amazon.com/

Kohei Enju (2):
  bpf: cpumap: propagate underlying error in cpu_map_update_elem()
  selftests/bpf: add tests for attaching invalid fd

 kernel/bpf/cpumap.c                           | 21 ++++++++++++-------
 .../bpf/prog_tests/xdp_cpumap_attach.c        | 19 +++++++++++++++--
 2 files changed, 30 insertions(+), 10 deletions(-)

-- 
2.51.0

[PATCH bpf-next v2 1/2] bpf: cpumap: propagate underlying error in cpu_map_update_elem()

[Kohei Enju]

After commit 9216477449f3 ("bpf: cpumap: Add the possibility to attach
an eBPF program to cpumap"), __cpu_map_entry_alloc() may fail with
errors other than -ENOMEM, such as -EBADF or -EINVAL.

However, __cpu_map_entry_alloc() returns NULL on all failures, and
cpu_map_update_elem() unconditionally converts this NULL into -ENOMEM.
As a result, user space always receives -ENOMEM regardless of the actual
underlying error.

Examples of unexpected behavior:
  - Nonexistent fd  : -ENOMEM (should be -EBADF)
  - Non-BPF fd      : -ENOMEM (should be -EINVAL)
  - Bad attach type : -ENOMEM (should be -EINVAL)

Change __cpu_map_entry_alloc() to return ERR_PTR(err) instead of NULL
and have cpu_map_update_elem() propagate this error.

Signed-off-by: Kohei Enju <enjuk@amazon.com>
---
 kernel/bpf/cpumap.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index 703e5df1f4ef..04171fbc39cb 100644
--- a/kernel/bpf/cpumap.c
+++ b/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);
-- 
2.51.0

Re: [PATCH bpf-next v2 1/2] bpf: cpumap: propagate underlying error in cpu_map_update_elem()

[Toke Høiland-Jørgensen]

Kohei Enju <enjuk@amazon.com> writes:

> After commit 9216477449f3 ("bpf: cpumap: Add the possibility to attach
> an eBPF program to cpumap"), __cpu_map_entry_alloc() may fail with
> errors other than -ENOMEM, such as -EBADF or -EINVAL.
>
> However, __cpu_map_entry_alloc() returns NULL on all failures, and
> cpu_map_update_elem() unconditionally converts this NULL into -ENOMEM.
> As a result, user space always receives -ENOMEM regardless of the actual
> underlying error.
>
> Examples of unexpected behavior:
>   - Nonexistent fd  : -ENOMEM (should be -EBADF)
>   - Non-BPF fd      : -ENOMEM (should be -EINVAL)
>   - Bad attach type : -ENOMEM (should be -EINVAL)
>
> Change __cpu_map_entry_alloc() to return ERR_PTR(err) instead of NULL
> and have cpu_map_update_elem() propagate this error.
>
> Signed-off-by: Kohei Enju <enjuk@amazon.com>

Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>

[PATCH bpf-next v2 2/2] selftests/bpf: add tests for attaching invalid fd

[Kohei Enju]

Add test cases for situations where adding the following types of file
descriptors to a cpumap entry should fail:
- Non-BPF file descriptor (expect -EINVAL)
- Nonexistent file descriptor (expect -EBADF)

Also tighten the assertion for the expected error when adding a
non-BPF_XDP_CPUMAP program to a cpumap entry.

Signed-off-by: Kohei Enju <enjuk@amazon.com>
---
 .../bpf/prog_tests/xdp_cpumap_attach.c        | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_cpumap_attach.c b/tools/testing/selftests/bpf/prog_tests/xdp_cpumap_attach.c
index df27535995af..ad56e4370ce3 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_cpumap_attach.c
+++ b/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
-- 
2.51.0

Re: [PATCH bpf-next v2 2/2] selftests/bpf: add tests for attaching invalid fd

[Toke Høiland-Jørgensen]

Kohei Enju <enjuk@amazon.com> writes:

> Add test cases for situations where adding the following types of file
> descriptors to a cpumap entry should fail:
> - Non-BPF file descriptor (expect -EINVAL)
> - Nonexistent file descriptor (expect -EBADF)
>
> Also tighten the assertion for the expected error when adding a
> non-BPF_XDP_CPUMAP program to a cpumap entry.
>
> Signed-off-by: Kohei Enju <enjuk@amazon.com>

Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>

Re: [PATCH bpf-next v2 0/2] bpf: cpumap: improve error propagation in cpu_map_update_elem()

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Mon, 8 Dec 2025 22:14:30 +0900 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [bpf-next,v2,1/2] bpf: cpumap: propagate underlying error in cpu_map_update_elem()
    https://git.kernel.org/bpf/bpf-next/c/48e11bad9a1f
  - [bpf-next,v2,2/2] selftests/bpf: add tests for attaching invalid fd
    https://git.kernel.org/bpf/bpf-next/c/18352f8fae91

You are awesome, thank you!
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