ACPI / sysfs: fix acpi_get_table() leak / acpi-sysfs denial of service

Reading an ACPI table through the /sys/firmware/acpi/tables interface
more than 65,536 times leads to the following log message:

 ACPI Error: Table ffff88033595eaa8, Validation count is zero after increment
  (20170119/tbutils-423)

...and the table being unavailable until the next reboot. Add the
missing acpi_put_table() so the table ->validation_count is decremented
after each read.

Reported-by: Anush Seetharaman <anush.seetharaman@intel.com>
Fixes: 174cc7187e6f "ACPICA: Tables: Back port acpi_get_table_with_size() ..."
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Cc: 4.10+ <stable@vger.kernel.org> # 4.10+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
index cf05ae973381..5180fef9eb49 100644
--- a/drivers/acpi/sysfs.c
+++ b/drivers/acpi/sysfs.c
@@ -333,14 +333,17 @@ static ssize_t acpi_table_show(struct file *filp, struct kobject *kobj,
             container_of(bin_attr, struct acpi_table_attr, attr);
         struct acpi_table_header *table_header = NULL;
         acpi_status status;
+        ssize_t rc;
 
         status = acpi_get_table(table_attr->name, table_attr->instance,
                                 &table_header);
         if (ACPI_FAILURE(status))
                 return -ENODEV;
 
-        return memory_read_from_buffer(buf, count, &offset,
-                                       table_header, table_header->length);
+        rc = memory_read_from_buffer(buf, count, &offset, table_header,
+                        table_header->length);
+        acpi_put_table(table_header);
+        return rc;
 }
 
 static int acpi_table_attr_init(struct kobject *tables_obj,