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

[Andrey Konovalov]

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
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
==================================================================

[Andrey Konovalov]

On Thu, Apr 20, 2017 at 6:47 PM, Andrey Konovalov <andre...@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.

[Sabrina Dubroca]

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.

--
Sabrina