From 8ce48623f0cf3d632e32448411feddccb693d351 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 12 Oct 2016 19:01:45 +0200 Subject: [PATCH] ipv6: tcp: restore IP6CB for pktoptions skbs 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: [] dump_stack+0x12e/0x185 /lib/dump_stack.c:15 [< inline >] print_address_description /mm/kasan/report.c:204 [] kasan_report_error+0x48b/0x4b0 /mm/kasan/report.c:283 [< inline >] kasan_report /mm/kasan/report.c:303 [] __asan_report_load1_noabort+0x3e/0x40 /mm/kasan/report.c:321 [] ip6_datagram_recv_specific_ctl+0x13f1/0x15c0 /net/ipv6/datagram.c:687 [] ip6_datagram_recv_ctl+0x33/0x40 [] do_ipv6_getsockopt.isra.4+0xaec/0x2150 [] ipv6_getsockopt+0x116/0x230 [] tcp_getsockopt+0x82/0xd0 /net/ipv4/tcp.c:3035 [] sock_common_getsockopt+0x95/0xd0 /net/core/sock.c:2647 [< inline >] SYSC_getsockopt /net/socket.c:1776 [] SyS_getsockopt+0x142/0x230 /net/socket.c:1758 [] 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 Reported-by: Baozeng Ding Signed-off-by: David S. Miller --- net/ipv6/tcp_ipv6.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c index 54cf7197c7ab..5a27ab4eab39 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -1190,6 +1190,16 @@ 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, unless it is a TCP_LISTEN socket. * @@ -1319,6 +1329,7 @@ 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); @@ -1352,15 +1363,6 @@ static void tcp_v6_fill_cb(struct sk_buff *skb, const struct ipv6hdr *hdr, 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; -- 2.20.1