linux-kernel - [PATCH 2/3] sched/core: handle overflow in cpu_shares_write

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Date:   Wed, 27 Feb 2019 11:10:18 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] sched/core: handle overflow in cpu_shares_write_u64

Bit shift in scale_load() could overflow shares. This patch saturates
it to MAX_SHARES like following sched_group_set_shares().

Example:
# echo 9223372036854776832 > cpu.shares
# cat cpu.shares

Before patch: 1024
After pattch: 262144

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
---
 kernel/sched/core.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d8d76a65cfdd..a626fbd9fdc7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6502,6 +6502,8 @@ static void cpu_cgroup_attach(struct cgroup_taskset *tset)
 static int cpu_shares_write_u64(struct cgroup_subsys_state *css,
 				struct cftype *cftype, u64 shareval)
 {
+	if (shareval > scale_load_down(ULONG_MAX))
+		shareval = MAX_SHARES;
 	return sched_group_set_shares(css_tg(css), scale_load(shareval));
 }