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

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

From: Ammar Faizi <ammarfaizi2@gnuweeb.org>

@bp is a local variable, calling mce_threshold_remove_device() when
threshold_create_bank() fails will not free the @bp. Note that
mce_threshold_remove_device() frees the @bp only if it's already
stored in the @threshold_banks per-CPU variable.

At that point, the @threshold_banks per-CPU variable is still NULL,
so the mce_threshold_remove_device() will just be a no-op and the
@bp is leaked.

Fix this by storing @bp to @threshold_banks before the loop, so in
case we fail, mce_threshold_remove_device() will free the @bp.

This bug is introduced by commit 6458de97fc15530b544 ("x86/mce/amd:
Straighten CPU hotplug path") [1].

Link: https://lore.kernel.org/all/20200403161943.1458-6-bp@alien8.de [1]

v4:
  - Add the link to the commit reference again.

v3:
  - Fold in changes from Alviro, the previous version is still
    leaking @bank[n].

v2:
  - No changes.

Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
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>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---
 arch/x86/kernel/cpu/mce/amd.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
index 9f4b508886dd..a5ef161facd9 100644
--- a/arch/x86/kernel/cpu/mce/amd.c
+++ b/arch/x86/kernel/cpu/mce/amd.c
@@ -1346,19 +1346,23 @@ int mce_threshold_create_device(unsigned int cpu)
 	if (!bp)
 		return -ENOMEM;
 
+	/*
+	 * If we fail, mce_threshold_remove_device() will free the @bp
+	 * via @threshold_banks.
+	 */
+	this_cpu_write(threshold_banks, bp);
+
 	for (bank = 0; bank < numbanks; ++bank) {
 		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(cpu);
+			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;
 }
-- 
2.32.0