[PATCH v3] net/sched: act_gate: Limit the max value for cycletime

[Edward Adam Davis <eadavis@qq.com>]

If the user passes a cycletime value of 0xFFFFFFFFFFFFFFFFULL,
an overflow occurs during the assignment of cycle in gate_timer_func():

cycle = p->tcfg_cycletime; // overflow, cycle = -1

Since the local variable cycle is declared as ktime_t (i.e., s64),
the assignment overflows.

This leads to an incorrect calculation of the close_time value.
Ultimately, the new hrtimer expiry time becomes less than now, causing
__hrtimer_run_queues() to execute the "timer callback" for an excessively
long period, which triggers a soft lockup. [1]

Another factor is that the passed interval value is 1; while this accelerates
the problematic progression of close_time, it is not the decisive factor in
the issue described in [1].

Modify the cycletime range in the policy to (0, S64_MAX), when parsing
cycletime, ensuring its value does not exceed S64_MAX guarantees that the
hrtimer can correctly calculate a valid expiry time.

[1]
watchdog: BUG: soft lockup - CPU#1 stuck for 3s! [syz-executor291:5020]
pc : seqcount_lockdep_reader_access+0xd8/0xf8 include/linux/seqlock.h:76
Call trace:
 arch_local_irq_restore arch/arm64/include/asm/irqflags.h:195 [inline] (P)
 seqcount_lockdep_reader_access+0xd8/0xf8 include/linux/seqlock.h:75 (P)
 ktime_get+0x68/0x218 kernel/time/timekeeping.c:971
 gate_get_time+0x1c/0xa4 net/sched/act_gate.c:23
 gate_timer_func+0x1a8/0x390 net/sched/act_gate.c:101
 __run_hrtimer kernel/time/hrtimer.c:2032 [inline]
 __hrtimer_run_queues+0x314/0xbe0 kernel/time/hrtimer.c:2096
 hrtimer_run_softirq+0x15c/0x21c kernel/time/hrtimer.c:2113
 handle_softirqs+0x2ec/0xd98 kernel/softirq.c:622
 __do_softirq+0x14/0x20 kernel/softirq.c:656
 ____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:78
 call_on_irq_stack+0x30/0x48 arch/arm64/kernel/entry.S:885
 do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:83
 invoke_softirq kernel/softirq.c:503 [inline]
 __irq_exit_rcu+0x1ac/0x428 kernel/softirq.c:735
 irq_exit_rcu+0x14/0x84 kernel/softirq.c:752
 __el1_irq arch/arm64/kernel/entry-common.c:531 [inline]
 el1_interrupt+0x40/0x60 arch/arm64/kernel/entry-common.c:543
 el1h_64_irq_handler+0x18/0x24 arch/arm64/kernel/entry-common.c:548
 el1h_64_irq+0x6c/0x70 arch/arm64/kernel/entry.S:586
 __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:26 [inline] (P)
 arch_local_irq_enable arch/arm64/include/asm/irqflags.h:48 [inline] (P)
 __local_bh_enable_ip+0x1f0/0x35c kernel/softirq.c:455 (P)
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 __alloc_skb+0x1c8/0x610 net/core/skbuff.c:699
 alloc_skb include/linux/skbuff.h:1384 [inline]
 alloc_skb_with_frags+0xb8/0x690 net/core/skbuff.c:6775
 sock_alloc_send_pskb+0x740/0x850 net/core/sock.c:3012
 unix_dgram_sendmsg+0x434/0x1078 net/unix/af_unix.c:2137
 sock_sendmsg_nosec net/socket.c:775 [inline]

Fixes: a51c328df310 ("net: qos: introduce a gate control flow action")
Reported-by: syzbot+0054fed3dc9085390f51@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=0054fed3dc9085390f51
Tested-by: syzbot+0054fed3dc9085390f51@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
v1 -> v2: return -EINVAL with NL_SET_BAD_ATTR
v2 -> v3: using policy to limit cycletime range

 net/sched/act_gate.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/net/sched/act_gate.c b/net/sched/act_gate.c
index fdbfcaa3e2ab..4c4a0f80dec1 100644
--- a/net/sched/act_gate.c
+++ b/net/sched/act_gate.c
@@ -166,13 +166,19 @@ static const struct nla_policy entry_policy[TCA_GATE_ENTRY_MAX + 1] = {
 	[TCA_GATE_ENTRY_MAX_OCTETS]	= { .type = NLA_S32 },
 };
 
+static const struct netlink_range_validation_signed gate_cycle_time_range = {
+	.min = 0,
+	.max = S64_MAX,
+};
+
 static const struct nla_policy gate_policy[TCA_GATE_MAX + 1] = {
 	[TCA_GATE_PARMS]		=
 		NLA_POLICY_EXACT_LEN(sizeof(struct tc_gate)),
 	[TCA_GATE_PRIORITY]		= { .type = NLA_S32 },
 	[TCA_GATE_ENTRY_LIST]		= { .type = NLA_NESTED },
 	[TCA_GATE_BASE_TIME]		= { .type = NLA_U64 },
-	[TCA_GATE_CYCLE_TIME]		= { .type = NLA_U64 },
+	[TCA_GATE_CYCLE_TIME]		=
+		NLA_POLICY_FULL_RANGE_SIGNED(NLA_S64, &gate_cycle_time_range),
 	[TCA_GATE_CYCLE_TIME_EXT]	= { .type = NLA_U64 },
 	[TCA_GATE_FLAGS]		= { .type = NLA_U32 },
 	[TCA_GATE_CLOCKID]		= { .type = NLA_S32 },
@@ -501,6 +507,7 @@ static int tcf_gate_init(struct net *net, struct nlattr *nla,
 			cycle = ktime_add_ns(cycle, entry->interval);
 		cycletime = cycle;
 	}
+
 	p->tcfg_cycletime = cycletime;
 	p->tcfg_cycletime_ext = cycletime_ext;
 
-- 
2.43.0