ACPI: custom_method: fix a possible memory leak

BugLink: https://bugs.launchpad.net/bugs/1928825
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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
index dfe097d0720213b25807d7bc88ce0a33c49265d9..e7716c7b9be76d0d676353c8ba2df46c400dc100 100644 (file)
--- a/drivers/acpi/custom_method.c
+++ b/drivers/acpi/custom_method.c
@@ -44,6 +44,8 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
                                   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;