linux-kernel - [PATCH bpf-next] net: Fix slab-out-of-bounds in inet[6]_steal

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Message-Id: <20230809-bpf-next-v1-1-c1b80712e83b@isovalent.com>
Date:   Wed, 09 Aug 2023 09:33:53 +0100
From:   Lorenz Bauer <lmb@...valent.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kuniyuki Iwashima <kuniyu@...zon.com>,
        Martin KaFai Lau <martin.lau@...nel.org>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Lorenz Bauer <lmb@...valent.com>
Subject: [PATCH bpf-next] net: Fix slab-out-of-bounds in inet[6]_steal_sock

Kumar reported a KASAN splat in tcp_v6_rcv:

  bash-5.2# ./test_progs -t btf_skc_cls_ingress
  ...
  [   51.810085] BUG: KASAN: slab-out-of-bounds in tcp_v6_rcv+0x2d7d/0x3440
  [   51.810458] Read of size 2 at addr ffff8881053f038c by task test_progs/226

The problem is that inet[6]_steal_sock accesses sk->sk_protocol without
accounting for request sockets. I added the check to ensure that we only
every try to perform a reuseport lookup on a supported socket.

It turns out that this isn't necessary at all. struct sock_common contains
a skc_reuseport flag which indicates whether a socket is part of a
reuseport group. inet[6]_lookup_reuseport already check this flag,
so we can't execute an erroneous reuseport lookup by definition.

Remove the unnecessary assertions to fix the out of bounds access.

Fixes: 9c02bec95954 ("bpf, net: Support SO_REUSEPORT sockets with bpf_sk_assign")
Reported-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
Signed-off-by: Lorenz Bauer <lmb@...valent.com>
---
 include/net/inet6_hashtables.h | 10 ----------
 include/net/inet_hashtables.h  | 10 ----------
 2 files changed, 20 deletions(-)

diff --git a/include/net/inet6_hashtables.h b/include/net/inet6_hashtables.h
index 284b5ce7205d..f9907ed36d54 100644
--- a/include/net/inet6_hashtables.h
+++ b/include/net/inet6_hashtables.h
@@ -119,16 +119,6 @@ struct sock *inet6_steal_sock(struct net *net, struct sk_buff *skb, int doff,
 	if (!prefetched)
 		return sk;
 
-	if (sk->sk_protocol == IPPROTO_TCP) {
-		if (sk->sk_state != TCP_LISTEN)
-			return sk;
-	} else if (sk->sk_protocol == IPPROTO_UDP) {
-		if (sk->sk_state != TCP_CLOSE)
-			return sk;
-	} else {
-		return sk;
-	}
-
 	reuse_sk = inet6_lookup_reuseport(net, sk, skb, doff,
 					  saddr, sport, daddr, ntohs(dport),
 					  ehashfn);
diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
index 1177effabed3..57a46993383a 100644
--- a/include/net/inet_hashtables.h
+++ b/include/net/inet_hashtables.h
@@ -465,16 +465,6 @@ struct sock *inet_steal_sock(struct net *net, struct sk_buff *skb, int doff,
 	if (!prefetched)
 		return sk;
 
-	if (sk->sk_protocol == IPPROTO_TCP) {
-		if (sk->sk_state != TCP_LISTEN)
-			return sk;
-	} else if (sk->sk_protocol == IPPROTO_UDP) {
-		if (sk->sk_state != TCP_CLOSE)
-			return sk;
-	} else {
-		return sk;
-	}
-
 	reuse_sk = inet_lookup_reuseport(net, sk, skb, doff,
 					 saddr, sport, daddr, ntohs(dport),
 					 ehashfn);

---
base-commit: eb62e6aef940fcb1879100130068369d4638088f
change-id: 20230808-bpf-next-a442a095562b

Best regards,
-- 
Lorenz Bauer <lmb@...valent.com>