Merge branch 'support-freplace-prog-from-user-namespace'

Mykyta Yatsenko says:

====================
Support freplace prog from user namespace

From: Mykyta Yatsenko <yatsenko@meta.com>

Freplace programs can't be loaded from user namespace, as
bpf_program__set_attach_target() requires searching for target prog BTF,
which is locked under CAP_SYS_ADMIN.
This patch set enables this use case by:
1. Relaxing capable check in bpf's BPF_BTF_GET_FD_BY_ID, check for CAP_BPF
instead of CAP_SYS_ADMIN, support BPF token in attr argument.
2. Pass BPF token around libbpf from bpf_program__set_attach_target() to
bpf syscall where capable check is.
3. Validate positive/negative scenarios in selftests

This patch set is enabled by the recent libbpf change[1], that
introduced bpf_object__prepare() API. Calling bpf_object__prepare() for
freplace program before bpf_program__set_attach_target() initializes BPF
token, which is then passed to bpf syscall by libbpf.

[1] https://lore.kernel.org/all/20250303135752.158343-1-mykyta.yatsenko5@gmail.com/
====================

Link: https://patch.msgid.link/20250317174039.161275-1-mykyta.yatsenko5@gmail.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Author: anakryiko

include/uapi/linux/bpf.h

@@ -1652,6 +1652,7 @@ union bpf_attr {
 		};
 		__u32		next_id;
 		__u32		open_flags;
+		__s32		fd_by_id_token_fd;
 	};
 
 	struct { /* anonymous struct used by BPF_OBJ_GET_INFO_BY_FD */

kernel/bpf/syscall.c

@@ -4732,6 +4732,8 @@ static int bpf_prog_get_info_by_fd(struct file *file,
 	info.recursion_misses = stats.misses;
 
 	info.verified_insns = prog->aux->verified_insns;
+	if (prog->aux->btf)
+		info.btf_id = btf_obj_id(prog->aux->btf);
 
 	if (!bpf_capable()) {
 		info.jited_prog_len = 0;
@@ -4878,8 +4880,6 @@ static int bpf_prog_get_info_by_fd(struct file *file,
 		}
 	}
 
-	if (prog->aux->btf)
-		info.btf_id = btf_obj_id(prog->aux->btf);
 	info.attach_btf_id = prog->aux->attach_btf_id;
 	if (attach_btf)
 		info.attach_btf_obj_id = btf_obj_id(attach_btf);
@@ -5120,15 +5120,34 @@ static int bpf_btf_load(const union bpf_attr *attr, bpfptr_t uattr, __u32 uattr_
 	return btf_new_fd(attr, uattr, uattr_size);
 }
 
-#define BPF_BTF_GET_FD_BY_ID_LAST_FIELD btf_id
+#define BPF_BTF_GET_FD_BY_ID_LAST_FIELD fd_by_id_token_fd
 
 static int bpf_btf_get_fd_by_id(const union bpf_attr *attr)
 {
+	struct bpf_token *token = NULL;
+
 	if (CHECK_ATTR(BPF_BTF_GET_FD_BY_ID))
 		return -EINVAL;
 
-	if (!capable(CAP_SYS_ADMIN))
+	if (attr->open_flags & ~BPF_F_TOKEN_FD)
+		return -EINVAL;
+
+	if (attr->open_flags & BPF_F_TOKEN_FD) {
+		token = bpf_token_get_from_fd(attr->fd_by_id_token_fd);
+		if (IS_ERR(token))
+			return PTR_ERR(token);
+		if (!bpf_token_allow_cmd(token, BPF_BTF_GET_FD_BY_ID)) {
+			bpf_token_put(token);
+			token = NULL;
+		}
+	}
+
+	if (!bpf_token_capable(token, CAP_SYS_ADMIN)) {
+		bpf_token_put(token);
 		return -EPERM;
+	}
+
+	bpf_token_put(token);
 
 	return btf_get_fd_by_id(attr->btf_id);
 }

tools/include/uapi/linux/bpf.h

@@ -1652,6 +1652,7 @@ union bpf_attr {
 		};
 		__u32		next_id;
 		__u32		open_flags;
+		__s32		fd_by_id_token_fd;
 	};
 
 	struct { /* anonymous struct used by BPF_OBJ_GET_INFO_BY_FD */

tools/lib/bpf/bpf.c

@@ -1097,7 +1097,7 @@ int bpf_map_get_fd_by_id(__u32 id)
 int bpf_btf_get_fd_by_id_opts(__u32 id,
 			      const struct bpf_get_fd_by_id_opts *opts)
 {
-	const size_t attr_sz = offsetofend(union bpf_attr, open_flags);
+	const size_t attr_sz = offsetofend(union bpf_attr, fd_by_id_token_fd);
 	union bpf_attr attr;
 	int fd;
 
@@ -1107,6 +1107,7 @@ int bpf_btf_get_fd_by_id_opts(__u32 id,
 	memset(&attr, 0, attr_sz);
 	attr.btf_id = id;
 	attr.open_flags = OPTS_GET(opts, open_flags, 0);
+	attr.fd_by_id_token_fd = OPTS_GET(opts, token_fd, 0);
 
 	fd = sys_bpf_fd(BPF_BTF_GET_FD_BY_ID, &attr, attr_sz);
 	return libbpf_err_errno(fd);

tools/lib/bpf/bpf.h

@@ -487,9 +487,10 @@ LIBBPF_API int bpf_link_get_next_id(__u32 start_id, __u32 *next_id);
 struct bpf_get_fd_by_id_opts {
 	size_t sz; /* size of this struct for forward/backward compatibility */
 	__u32 open_flags; /* permissions requested for the operation on fd */
+	__u32 token_fd;
 	size_t :0;
 };
-#define bpf_get_fd_by_id_opts__last_field open_flags
+#define bpf_get_fd_by_id_opts__last_field token_fd
 
 LIBBPF_API int bpf_prog_get_fd_by_id(__u32 id);
 LIBBPF_API int bpf_prog_get_fd_by_id_opts(__u32 id,

tools/lib/bpf/btf.c

@@ -1619,12 +1619,18 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf)
 	return btf;
 }
 
-struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf)
+struct btf *btf_load_from_kernel(__u32 id, struct btf *base_btf, int token_fd)
 {
 	struct btf *btf;
 	int btf_fd;
+	LIBBPF_OPTS(bpf_get_fd_by_id_opts, opts);
+
+	if (token_fd) {
+		opts.open_flags |= BPF_F_TOKEN_FD;
+		opts.token_fd = token_fd;
+	}
 
-	btf_fd = bpf_btf_get_fd_by_id(id);
+	btf_fd = bpf_btf_get_fd_by_id_opts(id, &opts);
 	if (btf_fd < 0)
 		return libbpf_err_ptr(-errno);
 
@@ -1634,6 +1640,11 @@ struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf)
 	return libbpf_ptr(btf);
 }
 
+struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf)
+{
+	return btf_load_from_kernel(id, base_btf, 0);
+}
+
 struct btf *btf__load_from_kernel_by_id(__u32 id)
 {
 	return btf__load_from_kernel_by_id_split(id, NULL);

tools/lib/bpf/libbpf.c

@@ -10024,7 +10024,7 @@ int libbpf_find_vmlinux_btf_id(const char *name,
 	return libbpf_err(err);
 }
 
-static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
+static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd, int token_fd)
 {
 	struct bpf_prog_info info;
 	__u32 info_len = sizeof(info);
@@ -10044,7 +10044,7 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
 		pr_warn("The target program doesn't have BTF\n");
 		goto out;
 	}
-	btf = btf__load_from_kernel_by_id(info.btf_id);
+	btf = btf_load_from_kernel(info.btf_id, NULL, token_fd);
 	err = libbpf_get_error(btf);
 	if (err) {
 		pr_warn("Failed to get BTF %d of the program: %s\n", info.btf_id, errstr(err));
@@ -10127,7 +10127,7 @@ static int libbpf_find_attach_btf_id(struct bpf_program *prog, const char *attac
 			pr_warn("prog '%s': attach program FD is not set\n", prog->name);
 			return -EINVAL;
 		}
-		err = libbpf_find_prog_btf_id(attach_name, attach_prog_fd);
+		err = libbpf_find_prog_btf_id(attach_name, attach_prog_fd, prog->obj->token_fd);
 		if (err < 0) {
 			pr_warn("prog '%s': failed to find BPF program (FD %d) BTF ID for '%s': %s\n",
 				prog->name, attach_prog_fd, attach_name, errstr(err));
@@ -12923,7 +12923,7 @@ struct bpf_link *bpf_program__attach_freplace(const struct bpf_program *prog,
 	if (target_fd) {
 		LIBBPF_OPTS(bpf_link_create_opts, target_opts);
 
-		btf_id = libbpf_find_prog_btf_id(attach_func_name, target_fd);
+		btf_id = libbpf_find_prog_btf_id(attach_func_name, target_fd, prog->obj->token_fd);
 		if (btf_id < 0)
 			return libbpf_err_ptr(btf_id);
 
@@ -13744,7 +13744,7 @@ int bpf_program__set_attach_target(struct bpf_program *prog,
 
 	if (attach_prog_fd) {
 		btf_id = libbpf_find_prog_btf_id(attach_func_name,
-						 attach_prog_fd);
+						 attach_prog_fd, prog->obj->token_fd);
 		if (btf_id < 0)
 			return libbpf_err(btf_id);
 	} else {

tools/lib/bpf/libbpf_internal.h

@@ -409,6 +409,7 @@ int libbpf__load_raw_btf(const char *raw_types, size_t types_len,
 int btf_load_into_kernel(struct btf *btf,
 			 char *log_buf, size_t log_sz, __u32 log_level,
 			 int token_fd);
+struct btf *btf_load_from_kernel(__u32 id, struct btf *base_btf, int token_fd);
 
 struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf);
 void btf_get_kernel_prefix_kind(enum bpf_attach_type attach_type,

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

@@ -19,6 +19,7 @@
 #include "priv_prog.skel.h"
 #include "dummy_st_ops_success.skel.h"
 #include "token_lsm.skel.h"
+#include "priv_freplace_prog.skel.h"
 
 static inline int sys_mount(const char *dev_name, const char *dir_name,
 			    const char *type, unsigned long flags,
@@ -788,6 +789,84 @@ static int userns_obj_priv_prog(int mnt_fd, struct token_lsm *lsm_skel)
 	return 0;
 }
 
+static int userns_obj_priv_freplace_setup(int mnt_fd, struct priv_freplace_prog **fr_skel,
+					  struct priv_prog **skel, int *tgt_fd)
+{
+	LIBBPF_OPTS(bpf_object_open_opts, opts);
+	int err;
+	char buf[256];
+
+	/* use bpf_token_path to provide BPF FS path */
+	snprintf(buf, sizeof(buf), "/proc/self/fd/%d", mnt_fd);
+	opts.bpf_token_path = buf;
+	*skel = priv_prog__open_opts(&opts);
+	if (!ASSERT_OK_PTR(*skel, "priv_prog__open_opts"))
+		return -EINVAL;
+	err = priv_prog__load(*skel);
+	if (!ASSERT_OK(err, "priv_prog__load"))
+		return -EINVAL;
+
+	*fr_skel = priv_freplace_prog__open_opts(&opts);
+	if (!ASSERT_OK_PTR(*skel, "priv_freplace_prog__open_opts"))
+		return -EINVAL;
+
+	*tgt_fd = bpf_program__fd((*skel)->progs.xdp_prog1);
+	return 0;
+}
+
+/* Verify that freplace works from user namespace, because bpf token is loaded
+ * in bpf_object__prepare
+ */
+static int userns_obj_priv_freplace_prog(int mnt_fd, struct token_lsm *lsm_skel)
+{
+	struct priv_freplace_prog *fr_skel = NULL;
+	struct priv_prog *skel = NULL;
+	int err, tgt_fd;
+
+	err = userns_obj_priv_freplace_setup(mnt_fd, &fr_skel, &skel, &tgt_fd);
+	if (!ASSERT_OK(err, "setup"))
+		goto out;
+
+	err = bpf_object__prepare(fr_skel->obj);
+	if (!ASSERT_OK(err, "freplace__prepare"))
+		goto out;
+
+	err = bpf_program__set_attach_target(fr_skel->progs.new_xdp_prog2, tgt_fd, "xdp_prog1");
+	if (!ASSERT_OK(err, "set_attach_target"))
+		goto out;
+
+	err = priv_freplace_prog__load(fr_skel);
+	ASSERT_OK(err, "priv_freplace_prog__load");
+
+out:
+	priv_freplace_prog__destroy(fr_skel);
+	priv_prog__destroy(skel);
+	return err;
+}
+
+/* Verify that replace fails to set attach target from user namespace without bpf token */
+static int userns_obj_priv_freplace_prog_fail(int mnt_fd, struct token_lsm *lsm_skel)
+{
+	struct priv_freplace_prog *fr_skel = NULL;
+	struct priv_prog *skel = NULL;
+	int err, tgt_fd;
+
+	err = userns_obj_priv_freplace_setup(mnt_fd, &fr_skel, &skel, &tgt_fd);
+	if (!ASSERT_OK(err, "setup"))
+		goto out;
+
+	err = bpf_program__set_attach_target(fr_skel->progs.new_xdp_prog2, tgt_fd, "xdp_prog1");
+	if (ASSERT_ERR(err, "attach fails"))
+		err = 0;
+	else
+		err = -EINVAL;
+
+out:
+	priv_freplace_prog__destroy(fr_skel);
+	priv_prog__destroy(skel);
+	return err;
+}
+
 /* this test is called with BPF FS that doesn't delegate BPF_BTF_LOAD command,
  * which should cause struct_ops application to fail, as BTF won't be uploaded
  * into the kernel, even if STRUCT_OPS programs themselves are allowed
@@ -1004,12 +1083,28 @@ void test_token(void)
 	if (test__start_subtest("obj_priv_prog")) {
 		struct bpffs_opts opts = {
 			.cmds = bit(BPF_PROG_LOAD),
-			.progs = bit(BPF_PROG_TYPE_KPROBE),
+			.progs = bit(BPF_PROG_TYPE_XDP),
 			.attachs = ~0ULL,
 		};
 
 		subtest_userns(&opts, userns_obj_priv_prog);
 	}
+	if (test__start_subtest("obj_priv_freplace_prog")) {
+		struct bpffs_opts opts = {
+			.cmds = bit(BPF_BTF_LOAD) | bit(BPF_PROG_LOAD) | bit(BPF_BTF_GET_FD_BY_ID),
+			.progs = bit(BPF_PROG_TYPE_EXT) | bit(BPF_PROG_TYPE_XDP),
+			.attachs = ~0ULL,
+		};
+		subtest_userns(&opts, userns_obj_priv_freplace_prog);
+	}
+	if (test__start_subtest("obj_priv_freplace_prog_fail")) {
+		struct bpffs_opts opts = {
+			.cmds = bit(BPF_BTF_LOAD) | bit(BPF_PROG_LOAD) | bit(BPF_BTF_GET_FD_BY_ID),
+			.progs = bit(BPF_PROG_TYPE_EXT) | bit(BPF_PROG_TYPE_XDP),
+			.attachs = ~0ULL,
+		};
+		subtest_userns(&opts, userns_obj_priv_freplace_prog_fail);
+	}
 	if (test__start_subtest("obj_priv_btf_fail")) {
 		struct bpffs_opts opts = {
 			/* disallow BTF loading */

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

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC("freplace/xdp_prog1")
+int new_xdp_prog2(struct xdp_md *xd)
+{
+	return XDP_DROP;
+}