netdev - [PATCH bpf 1/2] xdp: check prog type before updating BPF link

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Message-Id: <20220107183049.311134-1-toke@redhat.com>
Date:   Fri,  7 Jan 2022 19:30:48 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        syzbot+983941aa85af6ded1fd9@...kaller.appspotmail.com,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH bpf 1/2] xdp: check prog type before updating BPF link

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@...kaller.appspotmail.com
Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
---
 net/core/dev.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index c4708e2487fb..2078d04c6482 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9656,6 +9656,12 @@ 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);
-- 
2.34.1