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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Mark Langsdorf <mlangsdo@redhat.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Subject: [PATCH 4.9 009/240] ACPI: custom_method: fix a possible memory leak
Date:   Thu, 20 May 2021 11:20:01 +0200
Message-Id: <20210520092108.917841282@linuxfoundation.org>
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From: Mark Langsdorf <mlangsdo@redhat.com>

commit 1cfd8956437f842836e8a066b40d1ec2fc01f13e upstream.

In cm_write(), if the 'buf' is allocated memory but not fully consumed,
it is possible to reallocate the buffer without freeing it by passing
'*ppos' as 0 on a subsequent call.

Add an explicit kfree() before kzalloc() to prevent the possible memory
leak.

Fixes: 526b4af47f44 ("ACPI: Split out custom_method functionality into an own driver")
Signed-off-by: Mark Langsdorf <mlangsdo@redhat.com>
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/acpi/custom_method.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/acpi/custom_method.c
+++ b/drivers/acpi/custom_method.c
@@ -37,6 +37,8 @@ static ssize_t cm_write(struct file *fil
 				   sizeof(struct acpi_table_header)))
 			return -EFAULT;
 		uncopied_bytes = max_size = table.length;
+		/* make sure the buf is not allocated */
+		kfree(buf);
 		buf = kzalloc(max_size, GFP_KERNEL);
 		if (!buf)
 			return -ENOMEM;