[PATCH stable 6.6 1/2] bpf: Reject sleepable kprobe_multi programs at attach time

[PATCH stable 6.6 1/2] bpf: Reject sleepable kprobe_multi programs at attach time

[Shung-Hsi Yu]

From: Varun R Mallya <varunrmallya@gmail.com>

commit eb7024bfcc5f68ed11ed9dd4891a3073c15f04a8 upstream.

kprobe.multi programs run in atomic/RCU context and cannot sleep.
However, bpf_kprobe_multi_link_attach() did not validate whether the
program being attached had the sleepable flag set, allowing sleepable
helpers such as bpf_copy_from_user() to be invoked from a non-sleepable
context.

This causes a "sleeping function called from invalid context" splat:

  BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:169
  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo
  preempt_count: 1, expected: 0
  RCU nest depth: 2, expected: 0

Fix this by rejecting sleepable programs early in
bpf_kprobe_multi_link_attach(), before any further processing.

Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Leon Hwang <leon.hwang@linux.dev>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20260401191126.440683-1-varunrmallya@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
[shung-hsi.yu: sleepable flag was in 'struct bpf_prog_aux' before commit
66c8473135c6 "bpf: move sleepable flag from bpf_prog_aux to bpf_prog"]
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
Checked that test_verifier and all flavors of test_progs in BPF
selftests still passes on x86_64 with the patchset applied[1].

1: https://github.com/kernel-patches/linux-stable/actions/runs/28080168542/job/83133064970
---
 kernel/trace/bpf_trace.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index a896b80252ae..87e7cc2dc5cc 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2905,6 +2905,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	if (prog->expected_attach_type != BPF_TRACE_KPROBE_MULTI)
 		return -EINVAL;
 
+	/* kprobe_multi is not allowed to be sleepable. */
+	if (prog->aux->sleepable)
+		return -EINVAL;
+
 	flags = attr->link_create.kprobe_multi.flags;
 	if (flags & ~BPF_F_KPROBE_MULTI_RETURN)
 		return -EINVAL;
-- 
2.54.0

[PATCH stable 6.6 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable

[Shung-Hsi Yu]

From: Varun R Mallya <varunrmallya@gmail.com>

commit c7cab53f9d5273f0cf2a26bdf178c4e074bdfb50 upstream.

Add a selftest to ensure that kprobe_multi programs cannot be attached
using the BPF_F_SLEEPABLE flag. This test succeeds when the kernel
rejects attachment of kprobe_multi when the BPF_F_SLEEPABLE flag is set.

Suggested-by: Leon Hwang <leon.hwang@linux.dev>
Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
Link: https://lore.kernel.org/r/20260408190137.101418-3-varunrmallya@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
[shung-hsi.yu: borrowed 'saved_error' variable from commit 00cdcd2900bd
("selftests/bpf: Don't use libbpf_get_error() in kprobe_multi_test"). ]
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 .../bpf/prog_tests/kprobe_multi_test.c        | 34 +++++++++++++++++++
 .../bpf/progs/kprobe_multi_sleepable.c        | 25 ++++++++++++++
 2 files changed, 59 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c

diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
index 4041cfa670eb..d41e140c3150 100644
--- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
+++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
@@ -4,6 +4,7 @@
 #include "trace_helpers.h"
 #include "kprobe_multi_empty.skel.h"
 #include "kprobe_multi_override.skel.h"
+#include "kprobe_multi_sleepable.skel.h"
 #include "bpf/libbpf_internal.h"
 #include "bpf/hashmap.h"
 
@@ -214,7 +215,9 @@ static void test_attach_api_syms(void)
 static void test_attach_api_fails(void)
 {
 	LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
 	struct kprobe_multi *skel = NULL;
+	struct kprobe_multi_sleepable *sl_skel = NULL;
 	struct bpf_link *link = NULL;
 	unsigned long long addrs[2];
 	const char *syms[2] = {
@@ -222,6 +225,7 @@ static void test_attach_api_fails(void)
 		"bpf_fentry_test2",
 	};
 	__u64 cookies[2];
+	int saved_error, err;
 
 	addrs[0] = ksym_get_addr("bpf_fentry_test1");
 	addrs[1] = ksym_get_addr("bpf_fentry_test2");
@@ -300,9 +304,39 @@ static void test_attach_api_fails(void)
 	if (!ASSERT_EQ(libbpf_get_error(link), -EINVAL, "fail_5_error"))
 		goto cleanup;
 
+	/* fail_9 - sleepable kprobe multi should not attach */
+	sl_skel = kprobe_multi_sleepable__open();
+	if (!ASSERT_OK_PTR(sl_skel, "sleep_skel_open"))
+		goto cleanup;
+
+	sl_skel->bss->user_ptr = sl_skel;
+
+	err = bpf_program__set_flags(sl_skel->progs.handle_kprobe_multi_sleepable,
+				     BPF_F_SLEEPABLE);
+	if (!ASSERT_OK(err, "sleep_skel_set_flags"))
+		goto cleanup;
+
+	err = kprobe_multi_sleepable__load(sl_skel);
+	if (!ASSERT_OK(err, "sleep_skel_load"))
+		goto cleanup;
+
+	link = bpf_program__attach_kprobe_multi_opts(sl_skel->progs.handle_kprobe_multi_sleepable,
+						     "bpf_fentry_test1", NULL);
+	saved_error = -errno;
+
+	if (!ASSERT_ERR_PTR(link, "fail_9"))
+		goto cleanup;
+
+	if (!ASSERT_EQ(saved_error, -EINVAL, "fail_9_error"))
+		goto cleanup;
+
+	err = bpf_prog_test_run_opts(bpf_program__fd(sl_skel->progs.fentry), &topts);
+	ASSERT_OK(err, "bpf_prog_test_run_opts");
+
 cleanup:
 	bpf_link__destroy(link);
 	kprobe_multi__destroy(skel);
+	kprobe_multi_sleepable__destroy(sl_skel);
 }
 
 static size_t symbol_hash(long key, void *ctx __maybe_unused)
diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c b/tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
new file mode 100644
index 000000000000..932e1d9c72e2
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+void *user_ptr = 0;
+
+SEC("kprobe.multi")
+int handle_kprobe_multi_sleepable(struct pt_regs *ctx)
+{
+	int a, err;
+
+	err = bpf_copy_from_user(&a, sizeof(a), user_ptr);
+	barrier_var(a);
+	return err;
+}
+
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(fentry)
+{
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.54.0

Re: [PATCH stable 6.6 1/2] bpf: Reject sleepable kprobe_multi programs at attach time

[Sasha Levin]

> [PATCH stable 6.6 1/2] bpf: Reject sleepable kprobe_multi programs at
> attach time
> [PATCH stable 6.6 2/2] selftests/bpf: Add test to ensure kprobe_multi
> is not sleepable

Queued the 2-patch series for 6.6, thanks! The prog->aux->sleepable
adaptation is right for 6.6 - nice catch.

--
Thanks,
Sasha