[PATCH 4.17 078/220] of: overlay: validate offset from property fixups

[Greg Kroah-Hartman]

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Frank Rowand <frank.row...@sony.com>

commit 482137bf2aecd887ebfa8756456764a2f6a0e545 upstream.

The smatch static checker marks the data in offset as untrusted,
leading it to warn:

  drivers/of/resolver.c:125 update_usages_of_a_phandle_reference()
  error: buffer underflow 'prop->value' 's32min-s32max'

Add check to verify that offset is within the property data.

Reported-by: Dan Carpenter <dan.carpen...@oracle.com>
Signed-off-by: Frank Rowand <frank.row...@sony.com>
Cc: <sta...@vger.kernel.org>
Signed-off-by: Rob Herring <r...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/of/resolver.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/of/resolver.c
+++ b/drivers/of/resolver.c
@@ -122,6 +122,11 @@ static int update_usages_of_a_phandle_re
                        goto err_fail;
                }
 
+               if (offset < 0 || offset + sizeof(__be32) > prop->length) {
+                       err = -EINVAL;
+                       goto err_fail;
+               }
+
                *(__be32 *)(prop->value + offset) = cpu_to_be32(phandle);
        }