linux-kernel - [PATCH] x86/intel_rdt: Fix locking in rdtgroup_schemata

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Date:   Tue, 11 Apr 2017 09:14:46 +0200
From:   Jiri Olsa <jolsa@...nel.org>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Peter Zijlstra <peterz@...radead.org>,
        Mike Galbraith <efault@....de>, Shaohua Li <shli@...com>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] x86/intel_rdt: Fix locking in rdtgroup_schemata_write

Currently we release the schemata lock before we free the
resource's temporary tmp_cbms allocation, which could be
already used another concurrent access and crashed like:

  BUG: unable to handle kernel NULL pointer dereference at           (null)
  IP: rdtgroup_schemata_write+0x2d1/0x460
  ...
  SNIP
  ...
  rdtgroup_file_write+0x1b/0x30
  kernfs_fop_write+0xe0/0x160
  vfs_write+0xbd/0x1e0
  SyS_write+0x7f/0xe0
  system_call_fastpath+0x16/0x1b

Moving the unlock after the release code.

Signed-off-by: Jiri Olsa <jolsa@...nel.org>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Mike Galbraith <efault@....de>
Cc: Shaohua Li <shli@...com>
---
 arch/x86/kernel/cpu/intel_rdt_schemata.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_schemata.c b/arch/x86/kernel/cpu/intel_rdt_schemata.c
index f369cb8db0d5..badd2b31a560 100644
--- a/arch/x86/kernel/cpu/intel_rdt_schemata.c
+++ b/arch/x86/kernel/cpu/intel_rdt_schemata.c
@@ -200,11 +200,11 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
 	}
 
 out:
-	rdtgroup_kn_unlock(of->kn);
 	for_each_enabled_rdt_resource(r) {
 		kfree(r->tmp_cbms);
 		r->tmp_cbms = NULL;
 	}
+	rdtgroup_kn_unlock(of->kn);
 	return ret ?: nbytes;
 }
 
-- 
2.9.3