From: Willem de Bruijn <will...@google.com>
Syzbot reported a read beyond the end of the skb head when returning
IPV6_ORIGDSTADDR:
BUG: KMSAN: kernel-infoleak in put_cmsg+0x5ef/0x860 net/core/scm.c:242
CPU: 0 PID: 4501 Comm: syz-executor128 Not tainted 4.17.0+ #9
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x185/0x1d0 lib/dump_stack.c:113
kmsan_report+0x188/0x2a0 mm/kmsan/kmsan.c:1125
kmsan_internal_check_memory+0x138/0x1f0 mm/kmsan/kmsan.c:1219
kmsan_copy_to_user+0x7a/0x160 mm/kmsan/kmsan.c:1261
copy_to_user include/linux/uaccess.h:184 [inline]
put_cmsg+0x5ef/0x860 net/core/scm.c:242
ip6_datagram_recv_specific_ctl+0x1cf3/0x1eb0 net/ipv6/datagram.c:719
ip6_datagram_recv_ctl+0x41c/0x450 net/ipv6/datagram.c:733
rawv6_recvmsg+0x10fb/0x1460 net/ipv6/raw.c:521
[..]
This logic and its ipv4 counterpart read the destination port from
the packet at skb_transport_offset(skb) + 4.
With MSG_MORE and a local SOCK_RAW sender, syzbot was able to cook a
packet that stores headers exactly up to skb_transport_offset(skb) in
the head and the remainder in a frag.
Avoid reading beyond skb->tail by testing skb_headlen(skb) instead of
skb->len when trying to access this field.
Link:
http://lkml.kernel.org/r/CAF=yd-lejwzj5a1-baaj2oy_hkmgygv6rsj_woraynv-fna...@mail.gmail.com
Reported-by: syzbot+9adb4b567003cac78...@syzkaller.appspotmail.com
Signed-off-by: Willem de Bruijn <will...@google.com>
---
net/ipv4/ip_sockglue.c | 2 +-
net/ipv6/datagram.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 64c76dcf7386..5f228d641d9b 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -152,7 +152,7 @@ static void ip_cmsg_recv_dstaddr(struct msghdr *msg, struct
sk_buff *skb)
const struct iphdr *iph = ip_hdr(skb);
__be16 *ports = (__be16 *)skb_transport_header(skb);
- if (skb_transport_offset(skb) + 4 > (int)skb->len)
+ if (skb_transport_offset(skb) + 4 > (int)skb_headlen(skb))
return;
/* All current transport protocols have the port numbers in the
diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
index 2ee08b6a86a4..fd43810aacd2 100644
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -702,7 +702,7 @@ void ip6_datagram_recv_specific_ctl(struct sock *sk, struct
msghdr *msg,
struct sockaddr_in6 sin6;
__be16 *ports = (__be16 *) skb_transport_header(skb);
- if (skb_transport_offset(skb) + 4 <= (int)skb->len) {
+ if (skb_transport_offset(skb) + 4 <= (int)skb_headlen(skb)) {
/* All current transport protocols have the port
numbers in the
* first four bytes of the transport header and this
function is
* written with this assumption in mind.
--
2.18.0.233.g985f88cf7e-goog
