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From: Willy Tarreau <w@1wt.eu>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        linux@roeck-us.net
Cc: Dave Jones <davej@codemonkey.org.uk>,
        "David S . Miller" <davem@davemloft.net>, Willy Tarreau <w@1wt.eu>
Subject: [PATCH 3.10 246/250] ipv6: handle -EFAULT from skb_copy_bits
Date: Thu,  8 Jun 2017 01:00:32 +0200
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From: Dave Jones <davej@codemonkey.org.uk>

commit a98f91758995cb59611e61318dddd8a6956b52c3 upstream.

By setting certain socket options on ipv6 raw sockets, we can confuse the
length calculation in rawv6_push_pending_frames triggering a BUG_ON.

RIP: 0010:[<ffffffff817c6390>] [<ffffffff817c6390>] rawv6_sendmsg+0xc30/0xc40
RSP: 0018:ffff881f6c4a7c18  EFLAGS: 00010282
RAX: 00000000fffffff2 RBX: ffff881f6c681680 RCX: 0000000000000002
RDX: ffff881f6c4a7cf8 RSI: 0000000000000030 RDI: ffff881fed0f6a00
RBP: ffff881f6c4a7da8 R08: 0000000000000000 R09: 0000000000000009
R10: ffff881fed0f6a00 R11: 0000000000000009 R12: 0000000000000030
R13: ffff881fed0f6a00 R14: ffff881fee39ba00 R15: ffff881fefa93a80

Call Trace:
 [<ffffffff8118ba23>] ? unmap_page_range+0x693/0x830
 [<ffffffff81772697>] inet_sendmsg+0x67/0xa0
 [<ffffffff816d93f8>] sock_sendmsg+0x38/0x50
 [<ffffffff816d982f>] SYSC_sendto+0xef/0x170
 [<ffffffff816da27e>] SyS_sendto+0xe/0x10
 [<ffffffff81002910>] do_syscall_64+0x50/0xa0
 [<ffffffff817f7cbc>] entry_SYSCALL64_slow_path+0x25/0x25

Handle by jumping to the failure path if skb_copy_bits gets an EFAULT.

Reproducer:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define LEN 504

int main(int argc, char* argv[])
{
	int fd;
	int zero = 0;
	char buf[LEN];

	memset(buf, 0, LEN);

	fd = socket(AF_INET6, SOCK_RAW, 7);

	setsockopt(fd, SOL_IPV6, IPV6_CHECKSUM, &zero, 4);
	setsockopt(fd, SOL_IPV6, IPV6_DSTOPTS, &buf, LEN);

	sendto(fd, buf, 1, 0, (struct sockaddr *) buf, 110);
}

Signed-off-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
 net/ipv6/raw.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index 464b1c9..989bd79 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -578,8 +578,11 @@ static int rawv6_push_pending_frames(struct sock *sk, struct flowi6 *fl6,
 	}
 
 	offset += skb_transport_offset(skb);
-	if (skb_copy_bits(skb, offset, &csum, 2))
-		BUG();
+	err = skb_copy_bits(skb, offset, &csum, 2);
+	if (err < 0) {
+		ip6_flush_pending_frames(sk);
+		goto out;
+	}
 
 	/* in case cksum was not initialized */
 	if (unlikely(csum))
-- 
2.8.0.rc2.1.gbe9624a