net: asix: fix uninit value bugs

mainline inclusion
from mainline-v5.14-rc7
commit a786e319
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I95RDW
CVE: CVE-2021-47101

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a786e3195d6af183033e86f0518ffd2c51c0e8ac



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

Syzbot reported uninit-value in asix_mdio_read(). The problem was in
missing error handling. asix_read_cmd() should initialize passed stack
variable smsr, but it can fail in some cases. Then while condidition
checks possibly uninit smsr variable.

Since smsr is uninitialized stack variable, driver can misbehave,
because smsr will be random in case of asix_read_cmd() failure.
Fix it by adding error handling and just continue the loop instead of
checking uninit value.

Added helper function for checking Host_En bit, since wrong loop was used
in 4 functions and there is no need in copy-pasting code parts.

Cc: Robert Foss <robert.foss@collabora.com>
Fixes: d9fe64e5 ("net: asix: Add in_pm parameter")
Reported-by:  <syzbot+a631ec9e717fb0423053@syzkaller.appspotmail.com>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Cheng Yu <serein.chengyu@huawei.com>