From 26467b0f8407cbd628fa5b7bcfd156e772004155 Mon Sep 17 00:00:00 2001 From: Xiaochen Shen Date: Tue, 29 Oct 2019 13:25:02 +0800 Subject: 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 Signed-off-by: Borislav Petkov Reviewed-by: Fenghua Yu Reviewed-by: Tony Luck Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: pei.p.jia@intel.com Cc: Reinette Chatre Cc: Thomas Gleixner Cc: x86-ml 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(+) (limited to 'arch') diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c index efbd54cc4e69..055c8613b531 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; -- cgit