linux-kernel - [tip: x86/urgent] x86/resctrl: Prevent NULL pointer dereference when reading mondata

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Message-ID: <157280114858.29376.4595330962343256563.tip-bot2@tip-bot2>
Date:   Sun, 03 Nov 2019 17:12:28 -0000
From:   "tip-bot2 for Xiaochen Shen" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     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>, Ingo Molnar <mingo@...nel.org>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/resctrl: Prevent NULL pointer dereference when
 reading mondata

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     26467b0f8407cbd628fa5b7bcfd156e772004155
Gitweb:        https://git.kernel.org/tip/26467b0f8407cbd628fa5b7bcfd156e772004155
Author:        Xiaochen Shen <xiaochen.shen@...el.com>
AuthorDate:    Tue, 29 Oct 2019 13:25:02 +08:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Sun, 03 Nov 2019 17:51:22 +01:00

x86/resctrl: Prevent NULL pointer dereference when reading mondata

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
---
 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 efbd54c..055c861 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;