[PATCH net] xfrm_user: prevent leaking 2 bytes of kernel memory

[Eric Dumazet <edumazet@google.com>]

struct xfrm_userpolicy_type has two holes, so we should not
use C99 style initializer.

KMSAN report:

BUG: KMSAN: kernel-infoleak in copyout lib/iov_iter.c:140 [inline]
BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x1b14/0x2800 lib/iov_iter.c:571
CPU: 1 PID: 4520 Comm: syz-executor841 Not tainted 4.17.0+ #5
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:1117
 kmsan_internal_check_memory+0x138/0x1f0 mm/kmsan/kmsan.c:1211
 kmsan_copy_to_user+0x7a/0x160 mm/kmsan/kmsan.c:1253
 copyout lib/iov_iter.c:140 [inline]
 _copy_to_iter+0x1b14/0x2800 lib/iov_iter.c:571
 copy_to_iter include/linux/uio.h:106 [inline]
 skb_copy_datagram_iter+0x422/0xfa0 net/core/datagram.c:431
 skb_copy_datagram_msg include/linux/skbuff.h:3268 [inline]
 netlink_recvmsg+0x6f1/0x1900 net/netlink/af_netlink.c:1959
 sock_recvmsg_nosec net/socket.c:802 [inline]
 sock_recvmsg+0x1d6/0x230 net/socket.c:809
 ___sys_recvmsg+0x3fe/0x810 net/socket.c:2279
 __sys_recvmmsg+0x58e/0xe30 net/socket.c:2391
 do_sys_recvmmsg+0x2a6/0x3e0 net/socket.c:2472
 __do_sys_recvmmsg net/socket.c:2485 [inline]
 __se_sys_recvmmsg net/socket.c:2481 [inline]
 __x64_sys_recvmmsg+0x15d/0x1c0 net/socket.c:2481
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x446ce9
RSP: 002b:00007fc307918db8 EFLAGS: 00000293 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00000000006dbc24 RCX: 0000000000446ce9
RDX: 000000000000000a RSI: 0000000020005040 RDI: 0000000000000003
RBP: 00000000006dbc20 R08: 0000000020004e40 R09: 0000000000000000
R10: 0000000040000000 R11: 0000000000000293 R12: 0000000000000000
R13: 00007ffc8d2df32f R14: 00007fc3079199c0 R15: 0000000000000001

Uninit was stored to memory at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:279 [inline]
 kmsan_save_stack mm/kmsan/kmsan.c:294 [inline]
 kmsan_internal_chain_origin+0x12b/0x210 mm/kmsan/kmsan.c:685
 kmsan_memcpy_origins+0x11d/0x170 mm/kmsan/kmsan.c:527
 __msan_memcpy+0x109/0x160 mm/kmsan/kmsan_instr.c:413
 __nla_put lib/nlattr.c:569 [inline]
 nla_put+0x276/0x340 lib/nlattr.c:627
 copy_to_user_policy_type net/xfrm/xfrm_user.c:1678 [inline]
 dump_one_policy+0xbe1/0x1090 net/xfrm/xfrm_user.c:1708
 xfrm_policy_walk+0x45a/0xd00 net/xfrm/xfrm_policy.c:1013
 xfrm_dump_policy+0x1c0/0x2a0 net/xfrm/xfrm_user.c:1749
 netlink_dump+0x9b5/0x1550 net/netlink/af_netlink.c:2226
 __netlink_dump_start+0x1131/0x1270 net/netlink/af_netlink.c:2323
 netlink_dump_start include/linux/netlink.h:214 [inline]
 xfrm_user_rcv_msg+0x8a3/0x9b0 net/xfrm/xfrm_user.c:2577
 netlink_rcv_skb+0x37e/0x600 net/netlink/af_netlink.c:2448
 xfrm_netlink_rcv+0xb2/0xf0 net/xfrm/xfrm_user.c:2598
 netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
 netlink_unicast+0x1680/0x1750 net/netlink/af_netlink.c:1336
 netlink_sendmsg+0x104f/0x1350 net/netlink/af_netlink.c:1901
 sock_sendmsg_nosec net/socket.c:629 [inline]
 sock_sendmsg net/socket.c:639 [inline]
 ___sys_sendmsg+0xec8/0x1320 net/socket.c:2117
 __sys_sendmsg net/socket.c:2155 [inline]
 __do_sys_sendmsg net/socket.c:2164 [inline]
 __se_sys_sendmsg net/socket.c:2162 [inline]
 __x64_sys_sendmsg+0x331/0x460 net/socket.c:2162
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
Local variable description: ----upt.i@dump_one_policy
Variable was created at:
 dump_one_policy+0x78/0x1090 net/xfrm/xfrm_user.c:1689
 xfrm_policy_walk+0x45a/0xd00 net/xfrm/xfrm_policy.c:1013

Byte 130 of 137 is uninitialized
Memory access starts at ffff88019550407f

Fixes: c0144beaeca42 ("[XFRM] netlink: Use nla_put()/NLA_PUT() variantes")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
---
 net/xfrm/xfrm_user.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 080035f056d992c49f8cbcc776d579c9769c67eb..1e50b70ad668068235c9054f5b0c9ff0d938d07f 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -1671,9 +1671,11 @@ static inline unsigned int userpolicy_type_attrsize(void)
 #ifdef CONFIG_XFRM_SUB_POLICY
 static int copy_to_user_policy_type(u8 type, struct sk_buff *skb)
 {
-	struct xfrm_userpolicy_type upt = {
-		.type = type,
-	};
+	struct xfrm_userpolicy_type upt;
+
+	/* Sadly there are two holes in struct xfrm_userpolicy_type */
+	memset(&upt, 0, sizeof(upt));
+	upt.type = type;
 
 	return nla_put(skb, XFRMA_POLICY_TYPE, sizeof(upt), &upt);
 }
-- 
2.18.0.rc1.244.gcf134e6275-goog