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Subject[PATCH 5.3 039/135] x86/resctrl: Prevent NULL pointer dereference when reading mondata
From: Xiaochen Shen <>

[ Upstream commit 26467b0f8407cbd628fa5b7bcfd156e772004155 ]

When a mon group is being deleted, rdtgrp->flags is set to RDT_DELETED
in rdtgroup_rmdir_mon() firstly. The structure of rdtgrp will be freed
until rdtgrp->waitcount is dropped to 0 in rdtgroup_kn_unlock() later.

During the window of deleting a mon group, if an application calls
rdtgroup_mondata_show() to read mondata under this mon group,
'rdtgrp' returned from rdtgroup_kn_lock_live() is a NULL pointer when
rdtgrp->flags is RDT_DELETED. And then 'rdtgrp' is passed in this path:
rdtgroup_mondata_show() --> mon_event_read() --> mon_event_count().
Thus it results in NULL pointer dereference in mon_event_count().

Check 'rdtgrp' in rdtgroup_mondata_show(), and return -ENOENT
immediately when reading mondata during the window of deleting a mon

Fixes: d89b7379015f ("x86/intel_rdt/cqm: Add mon_data")
Signed-off-by: Xiaochen Shen <>
Signed-off-by: Borislav Petkov <>
Reviewed-by: Fenghua Yu <>
Reviewed-by: Tony Luck <>
Cc: "H. Peter Anvin" <>
Cc: Ingo Molnar <>
Cc: Reinette Chatre <>
Cc: Thomas Gleixner <>
Cc: x86-ml <>
Signed-off-by: Sasha Levin <>
arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index efbd54cc4e696..055c8613b5317 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -522,6 +522,10 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
int ret = 0;

rdtgrp = rdtgroup_kn_lock_live(of->kn);
+ if (!rdtgrp) {
+ ret = -ENOENT;
+ goto out;
+ }

md.priv = of->kn->priv;
resid = md.u.rid;

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