linux-kernel - [PATCH 4.19 021/321] x86/resctrl: Prevent NULL pointer dereference when reading mondata

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Message-Id: <20191203223428.221829108@linuxfoundation.org>
Date:   Tue,  3 Dec 2019 23:31:27 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xiaochen Shen <xiaochen.shen@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        pei.p.jia@...el.com, Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86-ml <x86@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 021/321] x86/resctrl: Prevent NULL pointer dereference when reading mondata

From: Xiaochen Shen <xiaochen.shen@...el.com>

[ 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
group.

Fixes: d89b7379015f ("x86/intel_rdt/cqm: Add mon_data")
Signed-off-by: Xiaochen Shen <xiaochen.shen@...el.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Fenghua Yu <fenghua.yu@...el.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: pei.p.jia@...el.com
Cc: Reinette Chatre <reinette.chatre@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: x86-ml <x86@...nel.org>
Link: https://lkml.kernel.org/r/1572326702-27577-1-git-send-email-xiaochen.shen@intel.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c b/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
index c8b72aff55e00..2052e1e6a11c9 100644
--- a/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
+++ b/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
@@ -459,6 +459,10 @@ 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;
-- 
2.20.1