Commit 749c202c authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Daniel Borkmann
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libbpf: Fix crash if SEC("freplace") programs don't have attach_prog_fd set 



Fix SIGSEGV caused by libbpf trying to find attach type in vmlinux BTF
for freplace programs. It's wrong to search in vmlinux BTF and libbpf
doesn't even mark vmlinux BTF as required for freplace programs. So
trying to search anything in obj->vmlinux_btf might cause NULL
dereference if nothing else in BPF object requires vmlinux BTF.

Instead, error out if freplace (EXT) program doesn't specify
attach_prog_fd during at the load time.

Fixes: 91abb4a6 ("libbpf: Support attachment of BPF tracing programs to kernel modules")
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220909193053.577111-3-andrii@kernel.org
parent cf060c2c

tools/lib/bpf/libbpf.c

+9 −4
Original line number Diff line number Diff line
@@ -9084,11 +9084,15 @@ static int libbpf_find_attach_btf_id(struct bpf_program *prog, const char *attac 
	int err = 0;



	/* BPF program's BTF ID */

	if (attach_prog_fd) {

	if (prog->type == BPF_PROG_TYPE_EXT || attach_prog_fd) {

		if (!attach_prog_fd) {

			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);

		if (err < 0) {

			pr_warn("failed to find BPF program (FD %d) BTF ID for '%s': %d\n",

				 attach_prog_fd, attach_name, err);

			pr_warn("prog '%s': failed to find BPF program (FD %d) BTF ID for '%s': %d\n",

				 prog->name, attach_prog_fd, attach_name, err);

			return err;

		}

		*btf_obj_fd = 0;
@@ -9105,7 +9109,8 @@ static int libbpf_find_attach_btf_id(struct bpf_program *prog, const char *attac 
		err = find_kernel_btf_id(prog->obj, attach_name, attach_type, btf_obj_fd, btf_type_id);

	}

	if (err) {

		pr_warn("failed to find kernel BTF type ID of '%s': %d\n", attach_name, err);

		pr_warn("prog '%s': failed to find kernel BTF type ID of '%s': %d\n",

			prog->name, attach_name, err);

		return err;

	}

	return 0;