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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Olivier Matz <olivier.matz@6wind.com>,
        Nicolas Dichtel <nicolas.dichtel@6wind.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.9 67/83] ipv6: fix EFAULT on sendto with icmpv6 and hdrincl
Date:   Sun,  9 Jun 2019 18:42:37 +0200
Message-Id: <20190609164133.500347042@linuxfoundation.org>
In-Reply-To: <20190609164127.843327870@linuxfoundation.org>
References: <20190609164127.843327870@linuxfoundation.org>
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From: Olivier Matz <olivier.matz@6wind.com>

[ Upstream commit b9aa52c4cb457e7416cc0c95f475e72ef4a61336 ]

The following code returns EFAULT (Bad address):

  s = socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6);
  setsockopt(s, SOL_IPV6, IPV6_HDRINCL, 1);
  sendto(ipv6_icmp6_packet, addr);   /* returns -1, errno = EFAULT */

The IPv4 equivalent code works. A workaround is to use IPPROTO_RAW
instead of IPPROTO_ICMPV6.

The failure happens because 2 bytes are eaten from the msghdr by
rawv6_probe_proto_opt() starting from commit 19e3c66b52ca ("ipv6
equivalent of "ipv4: Avoid reading user iov twice after
raw_probe_proto_opt""), but at that time it was not a problem because
IPV6_HDRINCL was not yet introduced.

Only eat these 2 bytes if hdrincl == 0.

Fixes: 715f504b1189 ("ipv6: add IPV6_HDRINCL option for raw sockets")
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/raw.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -880,11 +880,14 @@ static int rawv6_sendmsg(struct sock *sk
 	opt = ipv6_fixup_options(&opt_space, opt);
 
 	fl6.flowi6_proto = proto;
-	rfv.msg = msg;
-	rfv.hlen = 0;
-	err = rawv6_probe_proto_opt(&rfv, &fl6);
-	if (err)
-		goto out;
+
+	if (!hdrincl) {
+		rfv.msg = msg;
+		rfv.hlen = 0;
+		err = rawv6_probe_proto_opt(&rfv, &fl6);
+		if (err)
+			goto out;
+	}
 
 	if (!ipv6_addr_any(daddr))
 		fl6.daddr = *daddr;