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From:   Dongyang Zhan <zdyzztq@gmail.com>
Date:   Thu, 14 May 2020 11:59:42 +0800
Message-ID: <CAFSR4ctk4PgMcLGTx6Q7K2DzF+efpG2irnBcod1HZTEH7i6tRg@mail.gmail.com>
Subject: Fwd: Possible null pointer dereference caused by vmstat_start()
To:     linux-kernel@vger.kernel.org
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=E5=8F=91=E4=BB=B6=E4=BA=BA=EF=BC=9A Dongyang Zhan <zdyzztq@gmail.com>
Date: 2020=E5=B9=B45=E6=9C=883=E6=97=A5=E5=91=A8=E6=97=A5 =E4=B8=8B=E5=8D=
=881:45
Subject: Possible null pointer dereference caused by vmstat_start()
To: <fenghua.yu@intel.com>
Cc: <linux-kernel@vger.kernel.org>


In Linux 4.10.17, vmstat_start() stores the results of v =3D
kmalloc(stat_items_size, GFP_KERNEL) in m->private =3D v before security
check. If m->private is accessed, it may cause null pointer
dereference.

Source code link:
https://elixir.bootlin.com/linux/v4.10.17/source/mm/vmstat.c#L1465

Source code;
v =3D kmalloc(stat_items_size, GFP_KERNEL);
m->private =3D v; //stores v before check;
if (!v)
 return ERR_PTR(-ENOMEM);

Function rdtgroup_seqfile_show() in
arch/x86/kernel/cpu/intel_rdt_rdtgroup.c access this pointer without
check, which is a possible bug.

Link:
https://elixir.bootlin.com/linux/v4.10.17/source/arch/x86/kernel/cpu/intel_=
rdt_rdtgroup.c#150
Source Code
static int rdtgroup_seqfile_show(struct seq_file *m, void *arg)
{
struct kernfs_open_file *of =3D m->private;
struct rftype *rft =3D of->kn->priv; // without check;

if (rft->seq_show)
return rft->seq_show(of, m, arg);
return 0;
}