net_sched: avoid shift-out-of-bounds in tcindex_set_parms()

tc_index being 16bit wide, we need to check that TCA_TCINDEX_SHIFT
attribute is not silly.

UBSAN: shift-out-of-bounds in net/sched/cls_tcindex.c:260:29
shift exponent 255 is too large for 32-bit type 'int'
CPU: 0 PID: 8516 Comm: syz-executor228 Not tainted 5.10.0-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+0x107/0x163 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:395
 valid_perfect_hash net/sched/cls_tcindex.c:260 [inline]
 tcindex_set_parms.cold+0x1b/0x215 net/sched/cls_tcindex.c:425
 tcindex_change+0x232/0x340 net/sched/cls_tcindex.c:546
 tc_new_tfilter+0x13fb/0x21b0 net/sched/cls_api.c:2127
 rtnetlink_rcv_msg+0x8b6/0xb80 net/core/rtnetlink.c:5555
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2494
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x907/0xe40 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:672
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2336
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2390
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2423
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Link: https://lore.kernel.org/r/20210114185229.1742255-1-eric.dumazet@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/sched/cls_tcindex.c

@@ -366,9 +366,13 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
 	if (tb[TCA_TCINDEX_MASK])
 		cp->mask = nla_get_u16(tb[TCA_TCINDEX_MASK]);
 
-	if (tb[TCA_TCINDEX_SHIFT])
+	if (tb[TCA_TCINDEX_SHIFT]) {
 		cp->shift = nla_get_u32(tb[TCA_TCINDEX_SHIFT]);
-
+		if (cp->shift > 16) {
+			err = -EINVAL;
+			goto errout;
+		}
+	}
 	if (!cp->hash) {
 		/* Hash not specified, use perfect hash if the upper limit
 		 * of the hashing index is below the threshold.