netdev - [PATCH bpf] bpf: fix out-of-bounds read in __bpf_skc

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Message-Id: <20190521075238.26803-1-lmb@cloudflare.com>
Date:   Tue, 21 May 2019 08:52:38 +0100
From:   Lorenz Bauer <lmb@...udflare.com>
To:     netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.com
Cc:     joe@...valent.com, Lorenz Bauer <lmb@...udflare.com>
Subject: [PATCH bpf] bpf: fix out-of-bounds read in __bpf_skc_lookup

__bpf_skc_lookup takes a socket tuple and the length of the
tuple as an argument. Based on the length, it decides which
address family to pass to the helper function sk_lookup.

In case of AF_INET6, it fails to verify that the length
of the tuple is long enough. sk_lookup may therefore access
data past the end of the tuple.

Fixes: 6acc9b432e67 ("bpf: Add helper to retrieve socket in BPF")
Signed-off-by: Lorenz Bauer <lmb@...udflare.com>
---
 net/core/filter.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 55bfc941d17a..76f1d99640e2 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5304,7 +5304,13 @@ __bpf_skc_lookup(struct sk_buff *skb, struct bpf_sock_tuple *tuple, u32 len,
 	struct net *net;
 	int sdif;
 
-	family = len == sizeof(tuple->ipv4) ? AF_INET : AF_INET6;
+	if (len == sizeof(tuple->ipv4))
+		family = AF_INET;
+	else if (len == sizeof(tuple->ipv6))
+		family = AF_INET6;
+	else
+		return NULL;
+
 	if (unlikely(family == AF_UNSPEC || flags ||
 		     !((s32)netns_id < 0 || netns_id <= S32_MAX)))
 		goto out;
-- 
2.19.1