[tip:sched/core] sched/core: Handle overflow in cpu_shares_write_u64

[tip-bot for Konstantin Khlebnikov]

Commit-ID:  5b61d50ab4ef590f5e1d4df15cd2cea5f5715308
Gitweb:     https://git.kernel.org/tip/5b61d50ab4ef590f5e1d4df15cd2cea5f5715308
Author:     Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
AuthorDate: Wed, 27 Feb 2019 11:10:18 +0300
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 19 Apr 2019 13:42:10 +0200

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@xxxxxxxxxxxxxx>
Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/155125501891.293431.3345233332801109696.stgit@buzz
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/sched/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fb09eaad1d3a..685b1541ce51 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6507,6 +6507,8 @@ 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));
 }