[PATCH 5.14 066/151] libbpf: Fix segfault in light skeleton for objects without BTF

Greg Kroah-Hartman
2021-10-11T14:05:10Z

From: Kumar Kartikeya Dwivedi <memxor@gmail.com>

[ Upstream commit 4729445b47efebf089da4ccbcd1b116ffa2ad4af ]

When fed an empty BPF object, bpftool gen skeleton -L crashes at
btf__set_fd() since it assumes presence of obj->btf, however for
the sequence below clang adds no .BTF section (hence no BTF).

Reproducer:

$ touch a.bpf.c
$ clang -O2 -g -target bpf -c a.bpf.c
$ bpftool gen skeleton -L a.bpf.o
/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
/* THIS FILE IS AUTOGENERATED! */

struct a_bpf {
struct bpf_loader_ctx ctx;
Segmentation fault (core dumped)

The same occurs for files compiled without BTF info, i.e. without
clang's -g flag.

Fixes: 67234743736a (libbpf: Generate loader program out of BPF ELF file.)
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210930061634.1840768-1-memxor@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/lib/bpf/libbpf.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index d27e017ebfbe..f1bc09e606cd 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8115,7 +8115,8 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)

if (obj->gen_loader) {
/* reset FDs */
- btf__set_fd(obj->btf, -1);
+ if (obj->btf)
+ btf__set_fd(obj->btf, -1);
for (i = 0; i < obj->nr_maps; i++)
obj->maps[i].fd = -1;
if (!err)
--
2.33.0