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 9:07 AM, Ammar Faizi wrote:
> On 3/3/22 8:58 AM, Alviro Iskandar Setiawan wrote:
>> hi sir, i think this can be improved again, we can avoid calling
>> this_cpu_read(mce_num_banks) twice if we pass the numbanks as an
>> argument, plz review the changes below
> 
> OK, nice improvement. I will fold this in...
> 

It looks like this now. Yazen, Alviro, please review the
following patch. If you think it looks good, I will submit
it for the v5.

 From 91a447f837d502b7a040cd68f333fb98f4b941d9 Mon Sep 17 00:00:00 2001
From: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Date: Thu, 3 Mar 2022 09:22:17 +0700
Subject: [PATCH v5 2/2] x86/MCE/AMD: Fix memory leak when `threshold_create_bank()` fails

In mce_threshold_create_device(), if 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/remove device
function. Also, eliminate the "goto out_err". Just early return inside
the loop if 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 | 32 +++++++++++++++++++-------------
  1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
index 9f4b508886dd..e492efab68a2 100644
--- a/arch/x86/kernel/cpu/mce/amd.c
+++ b/arch/x86/kernel/cpu/mce/amd.c
@@ -1293,10 +1293,23 @@ static void threshold_remove_bank(struct threshold_bank *bank)
  	kfree(bank);
  }
  
+static void _mce_threshold_remove_device(struct threshold_bank **bp,
+					 unsigned int numbanks)
+{
+	unsigned int bank;
+
+	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 +1320,7 @@ 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, this_cpu_read(mce_num_banks));
  	return 0;
  }
  
@@ -1350,15 +1357,14 @@ 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, numbanks);
+			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