RE: [PATCH 4.9 04/20] net: Fix for_each_netdev_feature on Big endian

[Mehrtens, Hauke]

-----Original Message-----
From: Greg Kroah-Hartman [mailto:gregkh@xxxxxxxxxxxxxxxxxxx] 
Sent: Thursday, February 21, 2019 3:36 PM
To: linux-kernel@xxxxxxxxxxxxxxx
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; stable@xxxxxxxxxxxxxxx; Mehrtens, Hauke <hauke.mehrtens@xxxxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>
Subject: [PATCH 4.9 04/20] net: Fix for_each_netdev_feature on Big endian

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

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

From: Hauke Mehrtens <hauke.mehrtens@xxxxxxxxx>

[ Upstream commit 3b89ea9c5902acccdbbdec307c85edd1bf52515e ]

The features attribute is of type u64 and stored in the native endianes on the system. The for_each_set_bit() macro takes a pointer to a 32 bit array and goes over the bits in this area. On little Endian systems this also works with an u64 as the most significant bit is on the highest address, but on big endian the words are swapped. When we expect bit 15 here we get bit 47 (15 + 32).

This patch converts it more or less to its own for_each_set_bit() implementation which works on 64 bit integers directly. This is then completely in host endianness and should work like expected.

Fixes: fd867d51f ("net/core: generic support for disabling netdev features down stack")
Signed-off-by: Hauke Mehrtens <hauke.mehrtens@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/netdev_features.h |   23 +++++++++++++++++++++--
 net/core/dev.c                  |    4 ++--
 2 files changed, 23 insertions(+), 4 deletions(-)

Hi Greg,

This commit adds a missing include, I do not know if this really causes a compile problem:
https://git.kernel.org/linus/8681ef1f3d295bd3600315325f3b3396d76d02f6

It was also suggested to use a longer commit ID in the Fixes tag like this:
Fixes: fd867d51f889 ("net/core: generic support for disabling netdev features down stack")

Hauke