From: Eelco Chaudron <echaudro@redhat.com>
Date: Tue, 12 May 2020 11:04:40 +0200
Subject: libbpf: Fix probe code to return EPERM if encountered
Patch-mainline: v5.8-rc1
Git-commit: fd9eef1a132d1974405c3ebf9d5688ec5c51da94
References: bsc#1177028

When the probe code was failing for any reason ENOTSUP was returned, even
if this was due to not having enough lock space. This patch fixes this by
returning EPERM to the user application, so it can respond and increase
the RLIMIT_MEMLOCK size.

Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/158927424896.2342.10402475603585742943.stgit@ebuild
Acked-by: Gary Lin <glin@suse.com>
---
 tools/lib/bpf/libbpf.c |   36 +++++++++++++++++++++++++++++-------
 1 file changed, 29 insertions(+), 7 deletions(-)

--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3236,7 +3236,7 @@ int bpf_map__resize(struct bpf_map *map,
 }
 
 static int
-bpf_object__probe_name(struct bpf_object *obj)
+bpf_object__probe_loading(struct bpf_object *obj)
 {
 	struct bpf_load_program_attr attr;
 	char *cp, errmsg[STRERR_BUFSIZE];
@@ -3256,15 +3256,36 @@ bpf_object__probe_name(struct bpf_object
 
 	ret = bpf_load_program_xattr(&attr, NULL, 0);
 	if (ret < 0) {
-		cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
-		pr_warning("Error in %s():%s(%d). Couldn't load basic 'r0 = 0' BPF program.\n",
-			   __func__, cp, errno);
-		return -errno;
+		ret = errno;
+		cp = libbpf_strerror_r(ret, errmsg, sizeof(errmsg));
+		pr_warning("Error in %s():%s(%d). Couldn't load trivial BPF "
+			   "program. Make sure your kernel supports BPF "
+			   "(CONFIG_BPF_SYSCALL=y) and/or that RLIMIT_MEMLOCK is "
+			   "set to big enough value.\n", __func__, cp, ret);
+		return -ret;
 	}
 	close(ret);
 
-	/* now try the same program, but with the name */
+	return 0;
+}
+
+static int
+bpf_object__probe_name(struct bpf_object *obj)
+{
+	struct bpf_load_program_attr attr;
+	struct bpf_insn insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	int ret;
+
+	/* make sure loading with name works */
 
+	memset(&attr, 0, sizeof(attr));
+	attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
+	attr.insns = insns;
+	attr.insns_cnt = ARRAY_SIZE(insns);
+	attr.license = "GPL";
 	attr.name = "test";
 	ret = bpf_load_program_xattr(&attr, NULL, 0);
 	if (ret >= 0) {
@@ -5638,7 +5659,8 @@ int bpf_object__load_xattr(struct bpf_ob
 
 	obj->loaded = true;
 
-	err = bpf_object__probe_caps(obj);
+	err = bpf_object__probe_loading(obj);
+	err = err ? : bpf_object__probe_caps(obj);
 	err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
 	err = err ? : bpf_object__sanitize_and_load_btf(obj);
 	err = err ? : bpf_object__sanitize_maps(obj);