linux-kernel - [PATCH 4.17 211/324] bpf: fix sk_skb programs without skb->dev assigned

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Message-Id: <20180823075006.712464475@linuxfoundation.org>
Date:   Thu, 23 Aug 2018 09:54:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.17 211/324] bpf: fix sk_skb programs without skb->dev assigned

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: John Fastabend <john.fastabend@...il.com>

[ Upstream commit 0c6bc6e531a6db36f49622f1f115770160f7afb0 ]

Multiple BPF helpers in use by sk_skb programs calculate the max
skb length using the __bpf_skb_max_len function. However, this
calculates the max length using the skb->dev pointer which can be
NULL when an sk_skb program is paired with an sk_msg program.

To force this a sk_msg program needs to redirect into the ingress
path of a sock with an attach sk_skb program. Then the the sk_skb
program would need to call one of the helpers that adjust the skb
size.

To fix the null ptr dereference use SKB_MAX_ALLOC size if no dev
is available.

Fixes: 8934ce2fd081 ("bpf: sockmap redirect ingress support")
Signed-off-by: John Fastabend <john.fastabend@...il.com>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/core/filter.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2516,7 +2516,8 @@ static int bpf_skb_net_shrink(struct sk_

 static u32 __bpf_skb_max_len(const struct sk_buff *skb)
 {
-	return skb->dev->mtu + skb->dev->hard_header_len;
+	return skb->dev ? skb->dev->mtu + skb->dev->hard_header_len :
+			  SKB_MAX_ALLOC;
 }

 static int bpf_skb_adjust_net(struct sk_buff *skb, s32 len_diff)