bpf: Check validity of link->type in bpf_link_show_fdinfo()

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index fbe7f8e2b022c0396e8417dc7c9f8ddcd4ad2aff..b5d9bba738347ebccc7e51ed60bcff8e2ea6c9f8 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2427,16 +2427,21 @@ 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)