[PATCH 4.9 008/240] ACPI: custom_method: fix potential use-after-free issue

Greg Kroah-Hartman
2021-05-20T11:04:53Z

From: Mark Langsdorf <mlangsdo@redhat.com>

commit e483bb9a991bdae29a0caa4b3a6d002c968f94aa upstream.

In cm_write(), buf is always freed when reaching the end of the
function. If the requested count is less than table.length, the
allocated buffer will be freed but subsequent calls to cm_write() will
still try to access it.

Remove the unconditional kfree(buf) at the end of the function and
set the buf to NULL in the -EINVAL error path to match the rest of
function.

Fixes: 03d1571d9513 ("ACPI: custom_method: fix memory leaks")
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, 1 insertion(+), 1 deletion(-)

--- a/drivers/acpi/custom_method.c
+++ b/drivers/acpi/custom_method.c
@@ -50,6 +50,7 @@ static ssize_t cm_write(struct file *fil
(*ppos + count < count) ||
(count > uncopied_bytes)) {
kfree(buf);
+ buf = NULL;
return -EINVAL;
}

@@ -71,7 +72,6 @@ static ssize_t cm_write(struct file *fil
add_taint(TAINT_OVERRIDDEN_ACPI_TABLE, LOCKDEP_NOW_UNRELIABLE);
}

- kfree(buf);
return count;
}