netfilter: ipset: fix shift-out-of-bounds in htable_bits()

htable_bits() can call jhash_size(32) and trigger shift-out-of-bounds

UBSAN: shift-out-of-bounds in net/netfilter/ipset/ip_set_hash_gen.h:151:6
shift exponent 32 is too large for 32-bit type 'unsigned int'
CPU: 0 PID: 8498 Comm: syz-executor519
 Not tainted 5.10.0-rc7-next-20201208-syzkaller #0
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
 htable_bits net/netfilter/ipset/ip_set_hash_gen.h:151 [inline]
 hash_mac_create.cold+0x58/0x9b net/netfilter/ipset/ip_set_hash_gen.h:1524
 ip_set_create+0x610/0x1380 net/netfilter/ipset/ip_set_core.c:1115
 nfnetlink_rcv_msg+0xecc/0x1180 net/netfilter/nfnetlink.c:252
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2494
 nfnetlink_rcv+0x1ac/0x420 net/netfilter/nfnetlink.c:600
 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:2345
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2399
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2432
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

This patch replaces htable_bits() by simple fls(hashsize - 1) call:
it alone returns valid nbits both for round and non-round hashsizes.
It is normal to set any nbits here because it is validated inside
following htable_size() call which returns 0 for nbits>31.

Fixes: 1feab10("netfilter: ipset: Unified hash type generation")
Reported-by: syzbot+d66bfadebca46cf61a2b@syzkaller.appspotmail.com
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Acked-by: Jozsef Kadlecsik <kadlec@netfilter.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/ipset/ip_set_hash_gen.h

@@ -141,20 +141,6 @@ htable_size(u8 hbits)
 	return hsize * sizeof(struct hbucket *) + sizeof(struct htable);
 }
 
-/* Compute htable_bits from the user input parameter hashsize */
-static u8
-htable_bits(u32 hashsize)
-{
-	/* Assume that hashsize == 2^htable_bits */
-	u8 bits = fls(hashsize - 1);
-
-	if (jhash_size(bits) != hashsize)
-		/* Round up to the first 2^n value */
-		bits = fls(hashsize);
-
-	return bits;
-}
-
 #ifdef IP_SET_HASH_WITH_NETS
 #if IPSET_NET_COUNT > 1
 #define __CIDR(cidr, i)		(cidr[i])
@@ -1525,7 +1511,11 @@ IPSET_TOKEN(HTYPE, _create)(struct net *net, struct ip_set *set,
 	if (!h)
 		return -ENOMEM;
 
-	hbits = htable_bits(hashsize);
+	/* Compute htable_bits from the user input parameter hashsize.
+	 * Assume that hashsize == 2^htable_bits,
+	 * otherwise round up to the first 2^n value.
+	 */
+	hbits = fls(hashsize - 1);
 	hsize = htable_size(hbits);
 	if (hsize == 0) {
 		kfree(h);