Commit 9bf48fa1 authored by Quentin Monnet's avatar Quentin Monnet Committed by Andrii Nakryiko
Browse files

libbpf: Prevent null-pointer dereference when prog to load has no BTF 



In bpf_objec_load_prog(), there's no guarantee that obj->btf is non-NULL
when passing it to btf__fd(), and this function does not perform any
check before dereferencing its argument (as bpf_object__btf_fd() used to
do). As a consequence, we get segmentation fault errors in bpftool (for
example) when trying to load programs that come without BTF information.

v2: Keep btf__fd() in the fix instead of reverting to bpf_object__btf_fd().

Fixes: df7c3f7d ("libbpf: make uniform use of btf__fd() accessor inside libbpf")
Suggested-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarQuentin Monnet <qmo@kernel.org>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240314150438.232462-1-qmo@kernel.org
parent fe879bb4

tools/lib/bpf/libbpf.c

+3 −4
Original line number Diff line number Diff line
@@ -7317,9 +7317,9 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog 
	char *cp, errmsg[STRERR_BUFSIZE];

	size_t log_buf_size = 0;

	char *log_buf = NULL, *tmp;

	int btf_fd, ret, err;

	bool own_log_buf = true;

	__u32 log_level = prog->log_level;

	int ret, err;



	if (prog->type == BPF_PROG_TYPE_UNSPEC) {

		/*
@@ -7343,9 +7343,8 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog 
	load_attr.prog_ifindex = prog->prog_ifindex;



	/* specify func_info/line_info only if kernel supports them */

	btf_fd = btf__fd(obj->btf);

	if (btf_fd >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {

		load_attr.prog_btf_fd = btf_fd;

	if (obj->btf && btf__fd(obj->btf) >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {

		load_attr.prog_btf_fd = btf__fd(obj->btf);

		load_attr.func_info = prog->func_info;

		load_attr.func_info_rec_size = prog->func_info_rec_size;

		load_attr.func_info_cnt = prog->func_info_cnt;