linux-kernel - Re: [PATCH] PCI/sysfs: Fix double free in error path

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Message-ID: <20221007070735.GX986@pengutronix.de>
Date:   Fri, 7 Oct 2022 09:07:35 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     linux-pci@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] PCI/sysfs: Fix double free in error path

On Fri, Oct 07, 2022 at 08:56:18AM +0200, Sascha Hauer wrote:
> When pci_create_attr() fails then pci_remove_resource_files() is called
> which will iterate over the res_attr[_wc] arrays and frees every non
> NULL entry. To avoid a double free here we have to set the failed entry
> to NULL in pci_create_attr() when freeing it.
> 

You might consider applying this alternative version instead which IMO
looks a bit better.

Sascha

-------------------------------8<-----------------------------

>From fe8e0e6f914c14395c751b7dc165967b12427995 Mon Sep 17 00:00:00 2001
From: Sascha Hauer <s.hauer@...gutronix.de>
Date: Fri, 7 Oct 2022 07:35:35 +0200
Subject: [PATCH] PCI/sysfs: Fix double free in error path

When pci_create_attr() fails then pci_remove_resource_files() is called
which will iterate over the res_attr[_wc] arrays and frees every non
NULL entry. To avoid a double free here set the array entry only after
it's clear we successfully initialized it.

Fixes: b562ec8f74e4 ("PCI: Don't leak memory if sysfs_create_bin_file() fails")
Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
Cc: <stable@...r.kernel.org>
---
 drivers/pci/pci-sysfs.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index fc804e08e3cb5..6dd4050c9f2ed 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -1174,11 +1174,9 @@ static int pci_create_attr(struct pci_dev *pdev, int num, int write_combine)
 
 	sysfs_bin_attr_init(res_attr);
 	if (write_combine) {
-		pdev->res_attr_wc[num] = res_attr;
 		sprintf(res_attr_name, "resource%d_wc", num);
 		res_attr->mmap = pci_mmap_resource_wc;
 	} else {
-		pdev->res_attr[num] = res_attr;
 		sprintf(res_attr_name, "resource%d", num);
 		if (pci_resource_flags(pdev, num) & IORESOURCE_IO) {
 			res_attr->read = pci_read_resource_io;
@@ -1196,10 +1194,17 @@ static int pci_create_attr(struct pci_dev *pdev, int num, int write_combine)
 	res_attr->size = pci_resource_len(pdev, num);
 	res_attr->private = (void *)(unsigned long)num;
 	retval = sysfs_create_bin_file(&pdev->dev.kobj, res_attr);
-	if (retval)
+	if (retval) {
 		kfree(res_attr);
+		return retval;
+	}
+
+	if (write_combine)
+		pdev->res_attr_wc[num] = res_attr;
+	else
+		pdev->res_attr[num] = res_attr;
 
-	return retval;
+	return 0;
 }
 
 /**
-- 
2.30.2

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