From 4e765b4972af7b07adcb1feb16e7a525ce1f6b28 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Fri, 29 Dec 2017 18:15:23 -0600
Subject: [PATCH] af_key: fix buffer overread in parse_exthdrs()
Git-commit: 4e765b4972af7b07adcb1feb16e7a525ce1f6b28
Patch-mainline: v4.15-rc9
References: bsc#1051510

If a message sent to a PF_KEY socket ended with an incomplete extension
header (fewer than 4 bytes remaining), then parse_exthdrs() read past
the end of the message, into uninitialized memory.  Fix it by returning
-EINVAL in this case.

Reproducer: 

	#include <linux/pfkeyv2.h>
	#include <sys/socket.h>
	#include <unistd.h>

	int main()
	{
		int sock = socket(PF_KEY, SOCK_RAW, PF_KEY_V2);
		char buf[17] = { 0 };
		struct sadb_msg *msg = (void *)buf;

		msg->sadb_msg_version = PF_KEY_V2;
		msg->sadb_msg_type = SADB_DELETE;
		msg->sadb_msg_len = 2;

		write(sock, buf, 17);
	}

Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 net/key/af_key.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/key/af_key.c b/net/key/af_key.c
index 596499cc8b2f..d40861a048fe 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -516,6 +516,9 @@ static int parse_exthdrs(struct sk_buff *skb, const struct sadb_msg *hdr, void *
 		uint16_t ext_type;
 		int ext_len;
 
+		if (len < sizeof(*ehdr))
+			return -EINVAL;
+
 		ext_len  = ehdr->sadb_ext_len;
 		ext_len *= sizeof(uint64_t);
 		ext_type = ehdr->sadb_ext_type;
-- 
2.18.0