Subject: [PATCH][next] ethtool: ioctl: Fix out-of-bounds warning in store_link_ksettings_for_user()

From: "Gustavo A. R. Silva" <[email-masked]>
Date: Fri, 16 Apr 2021 15:15:40 -0500

Fix the following out-of-bounds warning:

net/ethtool/ioctl.c:492:2: warning: 'memcpy' offset [49, 84] from the object at 'link_usettings' is out of the bounds of referenced subobject 'base' with type 'struct ethtool_link_settings' at offset 0 [-Warray-bounds]

The problem is that the original code is trying to copy data into a
some struct members adjacent to each other in a single call to
memcpy(). This causes a legitimate compiler warning because memcpy()
overruns the length of &link_usettings.base. Fix this by directly
using &link_usettings and _from_ as destination and source addresses,
instead.

This helps with the ongoing efforts to globally enable -Warray-bounds
and get us closer to being able to tighten the FORTIFY_SOURCE routines
on memcpy().

Link: https://github.com/KSPP/linux/issues/109
Reported-by: kernel test robot <[email-masked]>
Signed-off-by: Gustavo A. R. Silva <[email-masked]>
---
 net/ethtool/ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index 27f1c5224acb..3fa7a394eabf 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -489,7 +489,7 @@ store_link_ksettings_for_user(void __user *to,
 {
 	struct ethtool_link_usettings link_usettings;
 
-	memcpy(&link_usettings.base, &from->base, sizeof(link_usettings));
+	memcpy(&link_usettings, from, sizeof(link_usettings));
 	bitmap_to_arr32(link_usettings.link_modes.supported,
 			from->link_modes.supported,
 			__ETHTOOL_LINK_MODE_MASK_NBITS);
-- 
2.27.0