Re: [PATCH v4 2/2] x86/mce/amd: Fix memory leak when `threshold_create_bank()` fails

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

On 3/3/22 6:20 AM, Ammar Faizi wrote:
> On 3/3/22 12:26 AM, Yazen Ghannam wrote:
>> Hi Ammar,
> 
> Hi Yazen,
> 
>> ...
>> The threshold interrupt handler uses this pointer. I think the goal here is to
>> set this pointer when the list is fully formed and clear this pointer before
>> making any changes to the list. Otherwise, the interrupt handler will operate
>> on incomplete data if an interrupt comes in the middle of these updates.
>>
>> The changes below should deal with memory leak issue while avoiding a race
>> with the threshold interrupt. What do you think?
> 
> Thanks for taking a look into this. I didn't notice that before. The
> changes look good to me, extra improvements:
> 
> 1) _mce_threshold_remove_device() should be static as we don't use it
>     in another translation unit.
> 2) Minor cleanup, we don't need "goto out_err", just early return
>     directly.
> 
> I will fold them in...
> 

Please review the patch below, if you think it looks good, I will
send this for the v5 series. I added your sign-off.

 From cae3965734a67d11a5286c612dfddf52398defc8 Mon Sep 17 00:00:00 2001
From: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Date: Thu, 3 Mar 2022 05:07:38 +0700
Subject: [PATCH v5 2/2] x86/MCE/AMD: Fix memory leak when `threshold_create_bank()` fails

In mce_threshold_create_device(), when threshold_create_bank() fails,
the @bp will be leaked, because mce_threshold_remove_device() will
not free the @bp. It only frees the @bp when we've already written
the @bp to the @threshold_banks per-CPU variable, but at the point,
we haven't.

Fix this by extracting the cleanup part into a new static function
_mce_threshold_remove_device(), then use it from create and remove
device function.

Also, eliminate the "goto out_err". Just early return inside the loop
when we fail.

Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: stable@vger.kernel.org # v5.8+
Fixes: 6458de97fc15 ("x86/mce/amd: Straighten CPU hotplug path")
Co-authored-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
Signed-off-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
Co-authored-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---
  arch/x86/kernel/cpu/mce/amd.c | 31 ++++++++++++++++++-------------
  1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
index 9f4b508886dd..ac7246a4de08 100644
--- a/arch/x86/kernel/cpu/mce/amd.c
+++ b/arch/x86/kernel/cpu/mce/amd.c
@@ -1293,10 +1293,22 @@ static void threshold_remove_bank(struct threshold_bank *bank)
  	kfree(bank);
  }
  
+static void _mce_threshold_remove_device(struct threshold_bank **bp)
+{
+	unsigned int bank, numbanks = this_cpu_read(mce_num_banks);
+
+	for (bank = 0; bank < numbanks; bank++) {
+		if (bp[bank]) {
+			threshold_remove_bank(bp[bank]);
+			bp[bank] = NULL;
+		}
+	}
+	kfree(bp);
+}
+
  int mce_threshold_remove_device(unsigned int cpu)
  {
  	struct threshold_bank **bp = this_cpu_read(threshold_banks);
-	unsigned int bank, numbanks = this_cpu_read(mce_num_banks);
  
  	if (!bp)
  		return 0;
@@ -1307,13 +1319,7 @@ int mce_threshold_remove_device(unsigned int cpu)
  	 */
  	this_cpu_write(threshold_banks, NULL);
  
-	for (bank = 0; bank < numbanks; bank++) {
-		if (bp[bank]) {
-			threshold_remove_bank(bp[bank]);
-			bp[bank] = NULL;
-		}
-	}
-	kfree(bp);
+	_mce_threshold_remove_device(bp);
  	return 0;
  }
  
@@ -1350,15 +1356,14 @@ int mce_threshold_create_device(unsigned int cpu)
  		if (!(this_cpu_read(bank_map) & (1 << bank)))
  			continue;
  		err = threshold_create_bank(bp, cpu, bank);
-		if (err)
-			goto out_err;
+		if (err) {
+			_mce_threshold_remove_device(bp);
+			return err;
+		}
  	}
  	this_cpu_write(threshold_banks, bp);
  
  	if (thresholding_irq_en)
  		mce_threshold_vector = amd_threshold_interrupt;
  	return 0;
-out_err:
-	mce_threshold_remove_device(cpu);
-	return err;
  }

-- 
Ammar Faizi