staging: gasket: Check the return value of gasket_get_bar_index()

Check the return value of gasket_get_bar_index function as it can return
a negative one (-EINVAL). If this happens, a negative index is used in
the "gasket_dev->bar_data" array.

Addresses-Coverity-ID: 1438542 ("Negative array index read")
Fixes: 9a69f50 ("drivers/staging: Gasket driver framework + Apex driver")
Signed-off-by: Oscar Carter <[email protected]>
Cc: stable <[email protected]>
Reviewed-by: Richard Yeh <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Oscar Carter

drivers/staging/gasket/gasket_core.c

@@ -925,6 +925,10 @@ do_map_region(const struct gasket_dev *gasket_dev, struct vm_area_struct *vma,
 		gasket_get_bar_index(gasket_dev,
 				     (vma->vm_pgoff << PAGE_SHIFT) +
 				     driver_desc->legacy_mmap_address_offset);
+
+	if (bar_index < 0)
+		return DO_MAP_REGION_INVALID;
+
 	phys_base = gasket_dev->bar_data[bar_index].phys_base + phys_offset;
 	while (mapped_bytes < map_length) {
 		/*