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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Lorenz Bauer <lmb@cloudflare.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Jakub Sitnicki <jakub@cloudflare.com>,
	Sasha Levin <sashal@kernel.org>,
	netdev@vger.kernel.org, bpf@vger.kernel.org
Subject: [PATCH AUTOSEL 5.5 135/542] bpf, sockmap: Check update requirements after locking
Date: Fri, 14 Feb 2020 10:42:07 -0500
Message-ID: <20200214154854.6746-135-sashal@kernel.org> (raw)
In-Reply-To: <20200214154854.6746-1-sashal@kernel.org>

From: Lorenz Bauer <lmb@cloudflare.com>

[ Upstream commit 85b8ac01a421791d66c3a458a7f83cfd173fe3fa ]

It's currently possible to insert sockets in unexpected states into
a sockmap, due to a TOCTTOU when updating the map from a syscall.
sock_map_update_elem checks that sk->sk_state == TCP_ESTABLISHED,
locks the socket and then calls sock_map_update_common. At this
point, the socket may have transitioned into another state, and
the earlier assumptions don't hold anymore. Crucially, it's
conceivable (though very unlikely) that a socket has become unhashed.
This breaks the sockmap's assumption that it will get a callback
via sk->sk_prot->unhash.

Fix this by checking the (fixed) sk_type and sk_protocol without the
lock, followed by a locked check of sk_state.

Unfortunately it's not possible to push the check down into
sock_(map|hash)_update_common, since BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB
run before the socket has transitioned from TCP_SYN_RECV into
TCP_ESTABLISHED.

Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20200207103713.28175-1-lmb@cloudflare.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/core/sock_map.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 058422b932607..b16ff3b8c6503 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -417,14 +417,16 @@ static int sock_map_update_elem(struct bpf_map *map, void *key,
 		ret = -EINVAL;
 		goto out;
 	}
-	if (!sock_map_sk_is_suitable(sk) ||
-	    sk->sk_state != TCP_ESTABLISHED) {
+	if (!sock_map_sk_is_suitable(sk)) {
 		ret = -EOPNOTSUPP;
 		goto out;
 	}
 
 	sock_map_sk_acquire(sk);
-	ret = sock_map_update_common(map, idx, sk, flags);
+	if (sk->sk_state != TCP_ESTABLISHED)
+		ret = -EOPNOTSUPP;
+	else
+		ret = sock_map_update_common(map, idx, sk, flags);
 	sock_map_sk_release(sk);
 out:
 	fput(sock->file);
@@ -740,14 +742,16 @@ static int sock_hash_update_elem(struct bpf_map *map, void *key,
 		ret = -EINVAL;
 		goto out;
 	}
-	if (!sock_map_sk_is_suitable(sk) ||
-	    sk->sk_state != TCP_ESTABLISHED) {
+	if (!sock_map_sk_is_suitable(sk)) {
 		ret = -EOPNOTSUPP;
 		goto out;
 	}
 
 	sock_map_sk_acquire(sk);
-	ret = sock_hash_update_common(map, key, sk, flags);
+	if (sk->sk_state != TCP_ESTABLISHED)
+		ret = -EOPNOTSUPP;
+	else
+		ret = sock_hash_update_common(map, key, sk, flags);
 	sock_map_sk_release(sk);
 out:
 	fput(sock->file);
-- 
2.20.1


  parent reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200214154854.6746-1-sashal@kernel.org>
2020-02-14 15:42 ` [PATCH AUTOSEL 5.5 133/542] bpftool: Don't crash on missing xlated program instructions Sasha Levin
2020-02-14 15:42 ` [PATCH AUTOSEL 5.5 134/542] bpf, sockhash: Synchronize_rcu before free'ing map Sasha Levin
2020-02-14 15:42 ` Sasha Levin [this message]
2020-02-14 15:42 ` [PATCH AUTOSEL 5.5 136/542] bpf: Improve bucket_log calculation logic Sasha Levin
2020-02-14 15:42 ` [PATCH AUTOSEL 5.5 137/542] bpf, sockmap: Don't sleep while holding RCU lock on tear-down Sasha Levin
2020-02-14 15:43 ` [PATCH AUTOSEL 5.5 212/542] samples/bpf: Set -fno-stack-protector when building BPF programs Sasha Levin
2020-02-14 15:44 ` [PATCH AUTOSEL 5.5 263/542] bpf: Print error message for bpftool cgroup show Sasha Levin
2020-02-14 15:44 ` [PATCH AUTOSEL 5.5 278/542] ice: add extra check for null Rx descriptor Sasha Levin
2020-02-14 15:44 ` [PATCH AUTOSEL 5.5 286/542] tools lib api fs: Fix gcc9 stringop-truncation compilation error Sasha Levin
2020-02-14 15:45 ` [PATCH AUTOSEL 5.5 352/542] bpf: Return -EBADRQC for invalid map type in __bpf_tx_xdp_map Sasha Levin
2020-02-14 15:47 ` [PATCH AUTOSEL 5.5 438/542] bpf, btf: Always output invariant hit in pahole DWARF to BTF transform Sasha Levin
2020-02-14 15:47 ` [PATCH AUTOSEL 5.5 461/542] selftests: bpf: Reset global state between reuseport test runs Sasha Levin
2020-02-14 15:47 ` [PATCH AUTOSEL 5.5 482/542] bpf: map_seq_next should always increase position index Sasha Levin
2020-02-14 15:48 ` [PATCH AUTOSEL 5.5 502/542] powerpc: Do not consider weak unresolved symbol relocations as bad Sasha Levin
2020-02-14 15:48 ` [PATCH AUTOSEL 5.5 535/542] i40e: Relax i40e_xsk_wakeup's return value when PF is busy Sasha Levin

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