net_sched: sch_fq: better validate TCA_FQ_WEIGHTS and TCA_FQ_PRIOMAP

syzbot was able to trigger the following report while providing
too small TCA_FQ_WEIGHTS attribute [1]

Fix is to use NLA_POLICY_EXACT_LEN() to ensure user space
provided correct sizes.

Apply the same fix to TCA_FQ_PRIOMAP.

[1]
BUG: KMSAN: uninit-value in fq_load_weights net/sched/sch_fq.c:960 [inline]
BUG: KMSAN: uninit-value in fq_change+0x1348/0x2fe0 net/sched/sch_fq.c:1071
fq_load_weights net/sched/sch_fq.c:960 [inline]
fq_change+0x1348/0x2fe0 net/sched/sch_fq.c:1071
fq_init+0x68e/0x780 net/sched/sch_fq.c:1159
qdisc_create+0x12f3/0x1be0 net/sched/sch_api.c:1326
tc_modify_qdisc+0x11ef/0x2c20
rtnetlink_rcv_msg+0x16a6/0x1840 net/core/rtnetlink.c:6558
netlink_rcv_skb+0x371/0x650 net/netlink/af_netlink.c:2545
rtnetlink_rcv+0x34/0x40 net/core/rtnetlink.c:6576
netlink_unicast_kernel net/netlink/af_netlink.c:1342 [inline]
netlink_unicast+0xf47/0x1250 net/netlink/af_netlink.c:1368
netlink_sendmsg+0x1238/0x13d0 net/netlink/af_netlink.c:1910
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
____sys_sendmsg+0x9c2/0xd60 net/socket.c:2588
___sys_sendmsg+0x28d/0x3c0 net/socket.c:2642
__sys_sendmsg net/socket.c:2671 [inline]
__do_sys_sendmsg net/socket.c:2680 [inline]
__se_sys_sendmsg net/socket.c:2678 [inline]
__x64_sys_sendmsg+0x307/0x490 net/socket.c:2678
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b

Uninit was created at:
slab_post_alloc_hook+0x129/0xa70 mm/slab.h:768
slab_alloc_node mm/slub.c:3478 [inline]
kmem_cache_alloc_node+0x5e9/0xb10 mm/slub.c:3523
kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:560
__alloc_skb+0x318/0x740 net/core/skbuff.c:651
alloc_skb include/linux/skbuff.h:1286 [inline]
netlink_alloc_large_skb net/netlink/af_netlink.c:1214 [inline]
netlink_sendmsg+0xb34/0x13d0 net/netlink/af_netlink.c:1885
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
____sys_sendmsg+0x9c2/0xd60 net/socket.c:2588
___sys_sendmsg+0x28d/0x3c0 net/socket.c:2642
__sys_sendmsg net/socket.c:2671 [inline]
__do_sys_sendmsg net/socket.c:2680 [inline]
__se_sys_sendmsg net/socket.c:2678 [inline]
__x64_sys_sendmsg+0x307/0x490 net/socket.c:2678
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b

CPU: 1 PID: 5001 Comm: syz-executor300 Not tainted 6.6.0-syzkaller-12401-g8f6f76a6 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023

Fixes: 29f834aa ("net_sched: sch_fq: add 3 bands and WRR scheduling")
Fixes: 49e7265f ("net_sched: sch_fq: add TCA_FQ_WEIGHTS attribute")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Jamal Hadi Salim<jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20231107160440.1992526-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/sched/sch_fq.c

@@ -919,14 +919,8 @@ static const struct nla_policy fq_policy[TCA_FQ_MAX + 1] = {
 	[TCA_FQ_TIMER_SLACK]		= { .type = NLA_U32 },
 	[TCA_FQ_HORIZON]		= { .type = NLA_U32 },
 	[TCA_FQ_HORIZON_DROP]		= { .type = NLA_U8 },
-	[TCA_FQ_PRIOMAP]		= {
-			.type = NLA_BINARY,
-			.len = sizeof(struct tc_prio_qopt),
-		},
-	[TCA_FQ_WEIGHTS]		= {
-			.type = NLA_BINARY,
-			.len = FQ_BANDS * sizeof(s32),
-		},
+	[TCA_FQ_PRIOMAP]		= NLA_POLICY_EXACT_LEN(sizeof(struct tc_prio_qopt)),
+	[TCA_FQ_WEIGHTS]		= NLA_POLICY_EXACT_LEN(FQ_BANDS * sizeof(s32)),
 };
 
 /* compress a u8 array with all elems <= 3 to an array of 2-bit fields */