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libbpf: Fix crash if SEC("freplace") programs don't have attach_prog_fd set

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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: 91abb4a6d7 ("libbpf: Support attachment of BPF tracing programs to kernel modules")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220909193053.577111-3-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2022-09-09 12:30:52 -07:00 committed by Daniel Borkmann
parent cf060c2c39
commit 749c202cb6
1 changed files with 9 additions and 4 deletions
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13
tools/lib/bpf/libbpf.c
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@ -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;