KASAN: stack-out-of-bounds Read in __nla_put

[syzbot]

Hello,

syzkaller hit the following crash on
fdddade65d7b5f8779374eb73d09889185280f60
git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers


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audit: type=1400 audit(1516082805.746:7): avc: denied { map } for
pid=3670 comm="syzkaller084676" path="/root/syzkaller084676122" dev="sda1"
ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
==================================================================
BUG: KASAN: stack-out-of-bounds in memcpy include/linux/string.h:344
[inline]
BUG: KASAN: stack-out-of-bounds in __nla_put+0x37/0x40 lib/nlattr.c:569
Read of size 255 at addr ffff8801c62f7968 by task syzkaller084676/3670

CPU: 1 PID: 3670 Comm: syzkaller084676 Not tainted
4.15.0-rc8-next-20180116+ #98
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x257 lib/dump_stack.c:53
print_address_description+0x73/0x250 mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report+0x23b/0x360 mm/kasan/report.c:412
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x137/0x190 mm/kasan/kasan.c:267
memcpy+0x23/0x50 mm/kasan/kasan.c:302
memcpy include/linux/string.h:344 [inline]
__nla_put+0x37/0x40 lib/nlattr.c:569
nla_put+0xf5/0x130 lib/nlattr.c:627
netlink_ack+0x78a/0xa10 net/netlink/af_netlink.c:2404
netlink_rcv_skb+0x2d1/0x400 net/netlink/af_netlink.c:2448
rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4548
netlink_unicast_kernel net/netlink/af_netlink.c:1308 [inline]
netlink_unicast+0x4c4/0x6b0 net/netlink/af_netlink.c:1334
netlink_sendmsg+0xa4a/0xe60 net/netlink/af_netlink.c:1897
sock_sendmsg_nosec net/socket.c:630 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:640
sock_write_iter+0x31a/0x5d0 net/socket.c:909
call_write_iter include/linux/fs.h:1775 [inline]
new_sync_write fs/read_write.c:469 [inline]
__vfs_write+0x684/0x970 fs/read_write.c:482
vfs_write+0x189/0x510 fs/read_write.c:544
SYSC_write fs/read_write.c:589 [inline]
SyS_write+0xef/0x220 fs/read_write.c:581
entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x43fce9
RSP: 002b:00007ffe2c7f0b68 EFLAGS: 00000217 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043fce9
RDX: 0000000000000022 RSI: 0000000020d1f000 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000004 R11: 0000000000000217 R12: 0000000000401650
R13: 00000000004016e0 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the page:
page:ffffea000718bdc0 count:0 mapcount:0 mapping: (null) index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: 0000000000000000 ffffea0007180101 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801c62f7880: f1 f1 f1 04 f2 f2 f2 f3 f3 f3 f3 00 00 00 00 00
ffff8801c62f7900: 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 00 00 00
> ffff8801c62f7980: f2 f2 f2 00 00 00 00 00 00 00 00 00 00 00 00 00
^
ffff8801c62f7a00: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 f2 f2 f2
ffff8801c62f7a80: f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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[Xin Long]

Hi, David A.

I guess you need to move up your memset(0) a little bit:

@@ -2427,6 +2443,7 @@ int netlink_rcv_skb(struct sk_buff *skb, int
(*cb)(struct sk_buff *,
nlh = nlmsg_hdr(skb);
err = 0;

+ memset(&extack, 0, sizeof(extack));
if (nlh->nlmsg_len < NLMSG_HDRLEN || skb->len < nlh->nlmsg_len)
return 0;

@@ -2438,7 +2455,6 @@ int netlink_rcv_skb(struct sk_buff *skb, int
(*cb)(struct sk_buff *,
if (nlh->nlmsg_type < NLMSG_MIN_TYPE)
goto ack;

- memset(&extack, 0, sizeof(extack));
err = cb(skb, nlh, &extack);

So that 'goto ack's won't skip it. :-)

[David Ahern]

On 1/17/18 2:39 AM, Xin Long wrote:
> I guess you need to move up your memset(0) a little bit:
>
> @@ -2427,6 +2443,7 @@ int netlink_rcv_skb(struct sk_buff *skb, int
> (*cb)(struct sk_buff *,
> nlh = nlmsg_hdr(skb);
> err = 0;
>
> + memset(&extack, 0, sizeof(extack));
> if (nlh->nlmsg_len < NLMSG_HDRLEN || skb->len < nlh->nlmsg_len)
> return 0;
>
> @@ -2438,7 +2455,6 @@ int netlink_rcv_skb(struct sk_buff *skb, int
> (*cb)(struct sk_buff *,
> if (nlh->nlmsg_type < NLMSG_MIN_TYPE)
> goto ack;
>
> - memset(&extack, 0, sizeof(extack));
> err = cb(skb, nlh, &extack);
>
> So that 'goto ack's won't skip it. :-)
>

you are correct. Can you submit a patch to do that?

[Xin Long]

sure, if you wish.