Re: [syzbot] UBSAN: shift-out-of-bounds in xfrm_selector_match

On Tue, Jun 15, 2021 at 7:32 AM Herbert Xu [off-list ref] wrote:

On Thu, Jun 10, 2021 at 12:19:26PM -0700, syzbot wrote:

quoted

Hello,

syzbot found the following issue on:

HEAD commit:    13c62f53 net/sched: act_ct: handle DNAT tuple collision
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=16635470300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=770708ea7cfd4916
dashboard link: https://syzkaller.appspot.com/bug?extid=e4c1dd36fc6b98c50859

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e4c1dd36fc6b98c50859@syzkaller.appspotmail.com

UBSAN: shift-out-of-bounds in ./include/net/xfrm.h:838:23
shift exponent -64 is negative
CPU: 0 PID: 12625 Comm: syz-executor.1 Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x141/0x1d7 lib/dump_stack.c:120
 ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
 __ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:327
 addr4_match include/net/xfrm.h:838 [inline]
 __xfrm4_selector_match net/xfrm/xfrm_policy.c:201 [inline]
 xfrm_selector_match.cold+0x35/0x3a net/xfrm/xfrm_policy.c:227
 xfrm_state_look_at+0x16d/0x440 net/xfrm/xfrm_state.c:1022

This appears to be an xfrm_state object with an IPv4 selector
that somehow has a prefixlen (d or s) of 96.

AFAICS this is not possible through xfrm_user.  OTOH it is not
obvious that af_key is entirely consistent in how it verifies
the prefix length, in particular, it seems to be possible for
two addresses with conflicting families to be provided as src/dst.

Can you confirm that this is indeed using af_key (a quick read
of the syzbot log seems to indicate that this is the case)?

Hi Herbert,

This was triggered by this program and, yes, it creates an AF_KEY socket:


18:01:48 executing program 1:
r0 = socket$inet_udp(0x2, 0x2, 0x0)
socket$key(0xf, 0x3, 0x2)
bind$inet(r0, &(0x7f00000001c0)={0x2, 0x0, @local}, 0x10)
socketpair$tipc(0x1e, 0x5, 0x0, &(0x7f00000000c0)={0xffffffffffffffff,
<r1=>0xffffffffffffffff})
ioctl$TUNSETLINK(r1, 0x8912, 0x400308)
connect$inet(r0, &(0x7f0000000480)={0x2, 0x0, @multicast2}, 0x10)
setsockopt$inet_IP_XFRM_POLICY(r0, 0x0, 0x11,
&(0x7f0000000080)={{{@in6=@ipv4={'\x00', '\xff\xff', @dev},
@in6=@private0, 0x0, 0xfffc, 0x0, 0x0, 0x2, 0x0, 0x0, 0x0, 0x0,
0xee01}, {0x2}, {}, 0x0, 0x0, 0x1}, {{@in, 0x0, 0x32}, 0x0,
@in6=@loopback, 0x0, 0x0, 0x0, 0xb7}}, 0xe8)
socket$key(0xf, 0x3, 0x2)
sendmmsg(r0, &(0x7f0000007fc0), 0x800001d, 0x0)