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    Subject[PATCH 4.14 011/209] x86/resctrl: Prevent NULL pointer dereference when reading mondata
    Date
    From: Xiaochen Shen <xiaochen.shen@intel.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@intel.com>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Reviewed-by: Fenghua Yu <fenghua.yu@intel.com>
    Reviewed-by: Tony Luck <tony.luck@intel.com>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: pei.p.jia@intel.com
    Cc: Reinette Chatre <reinette.chatre@intel.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: x86-ml <x86@kernel.org>
    Link: https://lkml.kernel.org/r/1572326702-27577-1-git-send-email-xiaochen.shen@intel.com
    Signed-off-by: Sasha Levin <sashal@kernel.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 f6ea94f8954a7..f892cb0b485e1 100644
    --- a/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
    +++ b/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
    @@ -313,6 +313,10 @@ 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


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