From 173dbe4fdb22e200e939d64b70c14910a9938ae0 Mon Sep 17 00:00:00 2001
From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Date: Fri, 24 Sep 2021 08:07:25 +0530
Subject: [PATCH] libbpf: Fix segfault in static linker for objects without BTF
Git-commit: bcfd367c2839f2126c048fe59700ec1b538e2b06
Patch-mainline: v5.15-rc4
References: stable-5.14.10

[ Upstream commit bcfd367c2839f2126c048fe59700ec1b538e2b06 ]

When a BPF object is compiled without BTF info (without -g),
trying to link such objects using bpftool causes a SIGSEGV due to
btf__get_nr_types accessing obj->btf which is NULL. Fix this by
checking for the NULL pointer, and return error.

Reproducer: 
$ cat a.bpf.c
extern int foo(void);
int bar(void) { return foo(); }
$ cat b.bpf.c
int foo(void) { return 0; }
$ clang -O2 -target bpf -c a.bpf.c
$ clang -O2 -target bpf -c b.bpf.c
$ bpftool gen obj out a.bpf.o b.bpf.o
Segmentation fault (core dumped)

After fix:
$ bpftool gen obj out a.bpf.o b.bpf.o
Libbpf: failed to find BTF info for object 'a.bpf.o'
Error: failed to link 'a.bpf.o': Unknown error -22 (-22)

Fixes: a46349227cd8 (libbpf: Add linker extern resolution support for functions and global variables)
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210924023725.70228-1-memxor@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 tools/lib/bpf/linker.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 10911a8cad0f..2df880cefdae 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -1649,11 +1649,17 @@ static bool btf_is_non_static(const struct btf_type *t)
 static int find_glob_sym_btf(struct src_obj *obj, Elf64_Sym *sym, const char *sym_name,
 			     int *out_btf_sec_id, int *out_btf_id)
 {
-	int i, j, n = btf__get_nr_types(obj->btf), m, btf_id = 0;
+	int i, j, n, m, btf_id = 0;
 	const struct btf_type *t;
 	const struct btf_var_secinfo *vi;
 	const char *name;
 
+	if (!obj->btf) {
+		pr_warn("failed to find BTF info for object '%s'\n", obj->filename);
+		return -EINVAL;
+	}
+
+	n = btf__get_nr_types(obj->btf);
 	for (i = 1; i <= n; i++) {
 		t = btf__type_by_id(obj->btf, i);
 
-- 
2.26.2