Merge branch 'bpf-fix-sleepable-check-for-tracing-lsm-prog'

Leon Hwang says:

====================
bpf: Fix sleepable check for tracing/lsm prog

When CONFIG_FUNCTION_ERROR_INJECTION is disabled, a sleepable tracing prog
is allowed to attach to '__x64_'-alike prefix symbols.

It is because the verifier does not verify whether the symbol is a kernel
function or a bpf prog. That said, a sleepable tracing prog is allowed to
attach to a bpf prog target whose name has '__x64_'-alike prefix.

For example, a sleepable fentry prog attaches to a '__x64_sys_nop' XDP
prog, and copies buffer from a user pointer with bpf_copy_from_user()
helper. After attaching the XDP prog to lo interface, the kernel BUG
could be triggered by 'ping -c 1 -W 1 127.0.0.1':

[    3.460756] BUG: sleeping function called from invalid context at kernel/bpf/trampoline.c:1324

Fix it by disallowing sleepable prog always when its target
btf is not kernel's btf.

Changes:
v3 -> v4:
* Move btf check outside of 'switch (prog->type)'. (per Andrii)
* v3: https://lore.kernel.org/bpf/20260804145710.43062-1-leon.hwang@linux.dev/

v2 -> v3:
* Use btf_is_kernel() instead of passing 'tgt_prog'. (per Andrii)
* v2: https://lore.kernel.org/bpf/20260725132624.78373-1-leon.hwang@linux.dev/

v1 -> v2:
* Drop redundant 'prog->sleepable' check. (per Viktor)
* Collect Acked-by from Viktor, Thanks.
* v1: https://lore.kernel.org/bpf/20260724141422.10463-1-leon.hwang@linux.dev/
====================

Link: https://patch.msgid.link/20260805150810.34907-1-leon.hwang@linux.dev
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

kernel/bpf/verifier.c

@@ -19022,6 +19022,9 @@ static int btf_id_allow_sleepable(u32 btf_id, unsigned long addr, const struct b
 	const struct btf_type *t;
 	const char *tname;
 
+	if (!btf_is_kernel(btf))
+		return -EINVAL;
+
 	switch (prog->type) {
 	case BPF_PROG_TYPE_TRACING:
 		t = btf_type_by_id(btf, btf_id);

tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c

@@ -5,6 +5,7 @@
 #include <bpf/btf.h>
 #include "bind4_prog.skel.h"
 #include "freplace_progmap.skel.h"
+#include "fentry_sleepable.skel.h"
 #include "xdp_dummy.skel.h"
 
 typedef int (*test_cb)(struct bpf_object *obj);
@@ -576,6 +577,60 @@ static void test_func_replace_progmap(void)
 	freplace_progmap__destroy(skel);
 }
 
+static void test_sleepable_fentry_to_xdp(void)
+{
+	struct fentry_sleepable *skel = NULL;
+	struct xdp_dummy *skel_xdp = NULL;
+	int ifindex, prog_fd, err;
+	char buff[64] = {};
+
+#ifndef __x86_64__
+	test__skip();
+	return;
+#endif
+
+	ifindex = if_nametoindex("lo");
+	if (!ASSERT_GT(ifindex, 0, "if_nametoindex"))
+		return;
+
+	skel_xdp = xdp_dummy__open_and_load();
+	if (!ASSERT_OK_PTR(skel_xdp, "xdp_dummy__open_and_load"))
+		return;
+
+	skel = fentry_sleepable__open();
+	if (!ASSERT_OK_PTR(skel, "fentry_sleepable__open"))
+		goto out;
+
+	skel->bss->user_ptr = buff;
+
+	prog_fd = bpf_program__fd(skel_xdp->progs.__x64_sys_nop);
+	err = bpf_program__set_attach_target(skel->progs.fentry_xdp, prog_fd, "__x64_sys_nop");
+	if (!ASSERT_OK(err, "bpf_program__set_attach_target"))
+		goto out;
+
+	err = fentry_sleepable__load(skel);
+	ASSERT_ERR(err, "fentry_sleepable__load");
+	if (err)
+		goto out;
+
+	skel->links.fentry_xdp = bpf_program__attach_trace(skel->progs.fentry_xdp);
+	if (!ASSERT_OK_PTR(skel->links.fentry_xdp, "bpf_program__attach_trace"))
+		goto out;
+
+	skel_xdp->links.__x64_sys_nop = bpf_program__attach_xdp(skel_xdp->progs.__x64_sys_nop,
+								ifindex);
+	if (!ASSERT_OK_PTR(skel_xdp->links.__x64_sys_nop, "bpf_program__attach_xdp"))
+		goto out;
+
+	err = system("ping -q -c 1 -W 1 127.0.0.1 > /dev/null");
+	ASSERT_OK(err, "ping");
+	ASSERT_ERR(skel->bss->retval, "retval");
+
+out:
+	fentry_sleepable__destroy(skel);
+	xdp_dummy__destroy(skel_xdp);
+}
+
 /* NOTE: affect other tests, must run in serial mode */
 void serial_test_fexit_bpf2bpf(void)
 {
@@ -607,4 +662,6 @@ void serial_test_fexit_bpf2bpf(void)
 		test_func_replace_int_with_void();
 	if (test__start_subtest("freplace_void"))
 		test_func_replace_void();
+	if (test__start_subtest("sleepable_fentry_to_xdp"))
+		test_sleepable_fentry_to_xdp();
 }

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

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char LICENSE[] SEC("license") = "GPL";
+
+void *user_ptr;
+int retval;
+
+SEC("fentry.s")
+int BPF_PROG(fentry_xdp)
+{
+	char buff[64];
+
+	retval = bpf_copy_from_user(buff, sizeof(buff), user_ptr);
+	return 0;
+}

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

@@ -10,4 +10,10 @@ int xdp_dummy_prog(struct xdp_md *ctx)
 	return XDP_PASS;
 }
 
+SEC("xdp")
+int __x64_sys_nop(struct xdp_md *ctx)
+{
+	return XDP_PASS;
+}
+
 char _license[] SEC("license") = "GPL";