[PATCH 5.4 19/56] sctp: break out if skb_header_pointer returns NULL in sctp_rcv_ootb

Greg Kroah-Hartman
2021-10-04T13:19:34Z

From: Xin Long <lucien.xin@gmail.com>

[ Upstream commit f7e745f8e94492a8ac0b0a26e25f2b19d342918f ]

We should always check if skb_header_pointer's return is NULL before
using it, otherwise it may cause null-ptr-deref, as syzbot reported:

KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
RIP: 0010:sctp_rcv_ootb net/sctp/input.c:705 [inline]
RIP: 0010:sctp_rcv+0x1d84/0x3220 net/sctp/input.c:196
Call Trace:
<IRQ>
sctp6_rcv+0x38/0x60 net/sctp/ipv6.c:1109
ip6_protocol_deliver_rcu+0x2e9/0x1ca0 net/ipv6/ip6_input.c:422
ip6_input_finish+0x62/0x170 net/ipv6/ip6_input.c:463
NF_HOOK include/linux/netfilter.h:307 [inline]
NF_HOOK include/linux/netfilter.h:301 [inline]
ip6_input+0x9c/0xd0 net/ipv6/ip6_input.c:472
dst_input include/net/dst.h:460 [inline]
ip6_rcv_finish net/ipv6/ip6_input.c:76 [inline]
NF_HOOK include/linux/netfilter.h:307 [inline]
NF_HOOK include/linux/netfilter.h:301 [inline]
ipv6_rcv+0x28c/0x3c0 net/ipv6/ip6_input.c:297

Fixes: 3acb50c18d8d ("sctp: delay as much as possible skb_linearize")
Reported-by: syzbot+581aff2ae6b860625116@syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sctp/input.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sctp/input.c b/net/sctp/input.c
index 2aca37717ed1..9616b600a876 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -676,7 +676,7 @@ static int sctp_rcv_ootb(struct sk_buff *skb)
ch = skb_header_pointer(skb, offset, sizeof(*ch), &_ch);

/* Break out if chunk length is less then minimal. */
- if (ntohs(ch->length) < sizeof(_ch))
+ if (!ch || ntohs(ch->length) < sizeof(_ch))
break;

ch_end = offset + SCTP_PAD4(ntohs(ch->length));
--
2.33.0