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.
Call pskb_may_pull before accessing the pointer to ensure that it lies
in skb head.
Link: http://lkml.kernel.org/r/CAF=yD-LEJwZj5a1-bAAj2Oy_hKmGygV6rsJ_WOrAYnv-fnayiQ@mail.gmail.com
Reported-by: syzbot+9adb4b567003cac781f0@syzkaller.appspotmail.com
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2efd4fca70