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

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

[Lorenz Bauer]

__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@cloudflare.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

Re: [PATCH bpf] bpf: fix out-of-bounds read in __bpf_skc_lookup

[Daniel Borkmann]

On 05/21/2019 09:52 AM, Lorenz Bauer wrote:
> __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@cloudflare.com>

Applied, thanks!