Re: net/xfrm: stack-out-of-bounds in xfrm_state_find

[Sabrina Dubroca <sd@queasysnail.net>]

2017-04-20, 19:30:27 +0200, Andrey Konovalov wrote:
> On Thu, Apr 20, 2017 at 6:47 PM, Andrey Konovalov <andreyknvl@google.com> wrote:
> > Hi,
> >
> > I've got the following error report while fuzzing the kernel with syzkaller.
> >
> > On linux-next commit 4f7d029b9bf009fbee76bb10c0c4351a1870d2f3 (4.11-rc7).
> >
> > A reproducer and .config are attached.
> >
> > ==================================================================
> > BUG: KASAN: stack-out-of-bounds in xfrm_state_find+0x2ce7/0x2f70 at
> > addr ffff88006654f790
> > Read of size 4 by task a.out/4065
> > page:ffffea00019953c0 count:0 mapcount:0 mapping:          (null) index:0x0
> > flags: 0x100000000000000()
> > raw: 0100000000000000 0000000000000000 0000000000000000 00000000ffffffff
> > raw: 0000000000000000 ffffea00019953e0 0000000000000000 0000000000000000
> > page dumped because: kasan: bad access detected
> > CPU: 1 PID: 4065 Comm: a.out Not tainted 4.11.0-rc7+ #251
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> > Call Trace:
> >  __dump_stack lib/dump_stack.c:16
> >  dump_stack+0x292/0x398 lib/dump_stack.c:52
> >  kasan_report_error mm/kasan/report.c:212
> >  kasan_report+0x4d8/0x510 mm/kasan/report.c:347
> >  __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:367
> >  xfrm_state_find+0x2ce7/0x2f70 net/xfrm/xfrm_state.c:897
> 
> I'm not sure if the line numbers in the report are correct.
> 
> My guess is that the guilty line is actually this one:
> 
> h = xfrm_dst_hash(net, daddr, saddr, tmpl->reqid, encap_family);
> 
> but I might be wrong.

I think you're right. From udp_sendmsg we can get a flowi4 allocated
on the stack, and that's where saddr and daddr come from (in
xfrm_tmpl_resolve_one). Then we feed that to xfrm_dst_hash(), but we
ignore family (AF_INET) and use encap_family (AF_INET6), and then
xfrm_dst_hash treats both addresses as if they were IPv6, so we read
past the end of the flowi4.

I don't know what the correct behavior would be.


BTW, I ran into a different stack-out-of-bounds (in
xfrm_dst_update_origin), also due to a flowi4 on stack being treated
as something bigger, I'll send the patch for that one.

> >  xfrm_tmpl_resolve_one net/xfrm/xfrm_policy.c:1470
> >  xfrm_tmpl_resolve+0x308/0xc90 net/xfrm/xfrm_policy.c:1514
> >  xfrm_resolve_and_create_bundle+0x16e/0x2590 net/xfrm/xfrm_policy.c:1889
> >  xfrm_lookup+0xd72/0x1170 net/xfrm/xfrm_policy.c:2253
> >  xfrm_lookup_route+0x39/0x1a0 net/xfrm/xfrm_policy.c:2375
> >  ip_route_output_flow+0x7f/0xa0 net/ipv4/route.c:2483
> >  udp_sendmsg+0x1565/0x2cd0 net/ipv4/udp.c:1015
> >  udpv6_sendmsg+0x8af/0x3500 net/ipv6/udp.c:1083
> >  inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:762
> >  sock_sendmsg_nosec net/socket.c:633
> >  sock_sendmsg+0xca/0x110 net/socket.c:643
> >  SYSC_sendto+0x660/0x810 net/socket.c:1696
> >  SyS_sendto+0x40/0x50 net/socket.c:1664
> >  entry_SYSCALL_64_fastpath+0x1f/0xc2 arch/x86/entry/entry_64.S:204
> > RIP: 0033:0x7f3daefd0b79
> > RSP: 002b:00007ffdb39bb0b8 EFLAGS: 00000206 ORIG_RAX: 000000000000002c
> > RAX: ffffffffffffffda RBX: 00007ffdb39bb210 RCX: 00007f3daefd0b79
> > RDX: 0000000000000000 RSI: 0000000020001000 RDI: 0000000000000003
> > RBP: 00000000004004a0 R08: 0000000020013ff0 R09: 0000000000000010
> > R10: 0000000020000000 R11: 0000000000000206 R12: 0000000000000000
> > R13: 00007ffdb39bb210 R14: 0000000000000000 R15: 0000000000000000
> > Memory state around the buggy address:
> >  ffff88006654f680: f1 f1 f1 00 f2 f2 f2 f2 f2 f2 f2 f8 f2 f2 f2 f2
> >  ffff88006654f700: f2 f2 f2 00 00 00 00 f2 f2 f2 f2 00 00 00 00 00
> >>ffff88006654f780: 00 00 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00 00
> >                          ^
> >  ffff88006654f800: f2 f2 f2 f3 f3 f3 f3 00 00 00 00 00 00 00 00 00
> >  ffff88006654f880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > ==================================================================

-- 
Sabrina