xdp: check prog type before updating BPF link

commit 382778edc8262b7535f00523e9eb22edba1b9816 upstream.

The bpf_xdp_link_update() function didn't check the program type before
updating the program, which made it possible to install any program type as
an XDP program, which is obviously not good. Syzbot managed to trigger this
by swapping in an LWT program on the XDP hook which would crash in a helper
call.

Fix this by adding a check and bailing out if the types don't match.

Fixes: 026a4c28e1db ("bpf, xdp: Implement LINK_UPDATE for BPF XDP link")
Reported-by: syzbot+983941aa85af6ded1fd9@syzkaller.appspotmail.com
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/20220107221115.326171-1-toke@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/core/dev.c b/net/core/dev.c
index e0878a500aa92b10533efa5dd74af11b57da9ae6..33dc2a3ff7d7802705e5b1fe828702f74a9f968f 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9636,6 +9636,12 @@ static int bpf_xdp_link_update(struct bpf_link *link, struct bpf_prog *new_prog,
                goto out_unlock;
        }
        old_prog = link->prog;
+       if (old_prog->type != new_prog->type ||
+           old_prog->expected_attach_type != new_prog->expected_attach_type) {
+               err = -EINVAL;
+               goto out_unlock;
+       }
+
        if (old_prog == new_prog) {
                /* no-op, don't disturb drivers */
                bpf_prog_put(new_prog);