From: Hou Tao houtao1@huawei.com

commit 8421d4c8762bd022cb491f2f0f7019ef51b4f0a7 upstream.

If a newly-added link type doesn't invoke BPF_LINK_TYPE(), accessing bpf_link_type_strs[link->type] may result in an out-of-bounds access.

To spot such missed invocations early in the future, checking the validity of link->type in bpf_link_show_fdinfo() and emitting a warning when such invocations are missed.

Signed-off-by: Hou Tao houtao1@huawei.com Signed-off-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/bpf/20241024013558.1135167-3-houtao@huaweicloud.com [ shung-hsi.yu: break up existing seq_printf() call since commit 68b04864ca42 ("bpf: Create links for BPF struct_ops maps.") is not present ] Signed-off-by: Shung-Hsi Yu shung-hsi.yu@suse.com --- kernel/bpf/syscall.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index f9906e5ad2e5..6455f80099cd 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -2816,16 +2816,21 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp) { const struct bpf_link *link = filp->private_data; const struct bpf_prog *prog = link->prog; + enum bpf_link_type type = link->type; char prog_tag[sizeof(prog->tag) * 2 + 1] = { };

+ if (type < ARRAY_SIZE(bpf_link_type_strs) && bpf_link_type_strs[type]) { + seq_printf(m, "link_type:\t%s\n", bpf_link_type_strs[type]); + } else { + WARN_ONCE(1, "missing BPF_LINK_TYPE(...) for link type %u\n", type); + seq_printf(m, "link_type:\t<%u>\n", type); + } + seq_printf(m, "link_id:\t%u\n", link->id); + bin2hex(prog_tag, prog->tag, sizeof(prog->tag)); seq_printf(m, - "link_type:\t%s\n" - "link_id:\t%u\n" "prog_tag:\t%s\n" "prog_id:\t%u\n", - bpf_link_type_strs[link->type], - link->id, prog_tag, prog->aux->id); if (link->ops->show_fdinfo)