[PATCH 3.18 015/145] [PATCH 084/760] ipv6: tcp: restore IP6CB for pktoptions skbs

Greg Kroah-Hartman
2017-04-16T11:22:29Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 8ce48623f0cf3d632e32448411feddccb693d351 ]

Baozeng Ding reported following KASAN splat :

BUG: KASAN: use-after-free in ip6_datagram_recv_specific_ctl+0x13f1/0x15c0 at addr ffff880029c84ec8
Read of size 1 by task poc/25548
Call Trace:
[<ffffffff82cf43c9>] dump_stack+0x12e/0x185 /lib/dump_stack.c:15
[< inline >] print_address_description /mm/kasan/report.c:204
[<ffffffff817ced3b>] kasan_report_error+0x48b/0x4b0 /mm/kasan/report.c:283
[< inline >] kasan_report /mm/kasan/report.c:303
[<ffffffff817ced9e>] __asan_report_load1_noabort+0x3e/0x40 /mm/kasan/report.c:321
[<ffffffff85c71da1>] ip6_datagram_recv_specific_ctl+0x13f1/0x15c0 /net/ipv6/datagram.c:687
[<ffffffff85c734c3>] ip6_datagram_recv_ctl+0x33/0x40
[<ffffffff85c0b07c>] do_ipv6_getsockopt.isra.4+0xaec/0x2150
[<ffffffff85c0c7f6>] ipv6_getsockopt+0x116/0x230
[<ffffffff859b5a12>] tcp_getsockopt+0x82/0xd0 /net/ipv4/tcp.c:3035
[<ffffffff855fb385>] sock_common_getsockopt+0x95/0xd0 /net/core/sock.c:2647
[< inline >] SYSC_getsockopt /net/socket.c:1776
[<ffffffff855f8ba2>] SyS_getsockopt+0x142/0x230 /net/socket.c:1758
[<ffffffff8685cdc5>] entry_SYSCALL_64_fastpath+0x23/0xc6
Memory state around the buggy address:
ffff880029c84d80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff880029c84e00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff880029c84e80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff880029c84f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff880029c84f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

He also provided a syzkaller reproducer.

Issue is that ip6_datagram_recv_specific_ctl() expects to find IP6CB
data that was moved at a different place in tcp_v6_rcv()

This patch moves tcp_v6_restore_cb() up and calls it from
tcp_v6_do_rcv() when np->pktoptions is set.

Fixes: 971f10eca186 ("tcp: better TCP_SKB_CB layout to reduce cache line misses")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Baozeng Ding <sploving1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv6/tcp_ipv6.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)

--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1250,6 +1250,16 @@ out:
return NULL;
}

+static void tcp_v6_restore_cb(struct sk_buff *skb)
+{
+ /* We need to move header back to the beginning if xfrm6_policy_check()
+ * and tcp_v6_fill_cb() are going to be called again.
+ * ip6_datagram_recv_specific_ctl() also expects IP6CB to be there.
+ */
+ memmove(IP6CB(skb), &TCP_SKB_CB(skb)->header.h6,
+ sizeof(struct inet6_skb_parm));
+}
+
/* The socket must have it's spinlock held when we get
* here.
*
@@ -1381,6 +1391,7 @@ ipv6_pktoptions:
np->flow_label = ip6_flowlabel(ipv6_hdr(opt_skb));
if (ipv6_opt_accepted(sk, opt_skb, &TCP_SKB_CB(opt_skb)->header.h6)) {
skb_set_owner_r(opt_skb, sk);
+ tcp_v6_restore_cb(opt_skb);
opt_skb = xchg(&np->pktoptions, opt_skb);
} else {
__kfree_skb(opt_skb);
@@ -1414,15 +1425,6 @@ static void tcp_v6_fill_cb(struct sk_buf
TCP_SKB_CB(skb)->sacked = 0;
}

-static void tcp_v6_restore_cb(struct sk_buff *skb)
-{
- /* We need to move header back to the beginning if xfrm6_policy_check()
- * and tcp_v6_fill_cb() are going to be called again.
- */
- memmove(IP6CB(skb), &TCP_SKB_CB(skb)->header.h6,
- sizeof(struct inet6_skb_parm));
-}
-
static int tcp_v6_rcv(struct sk_buff *skb)
{
const struct tcphdr *th;