Re: [PATCH] net: socket: fix a missing-check bug

Hi Wenwen,

On October 20, 2018 8:58:10 AM PDT, Wenwen Wang [off-list ref] wrote:

In ethtool_ioctl(), the ioctl command is firstly obtained from the
user-space buffer 'compat_rxnfc' through get_user() and saved to
'ethcmd'.
Then, 'ethcmd' is checked to see whether it is necessary to pre-process
the
ethool structure, because the structure ethtool_rxnfc is defined with
padding, as mentioned in the comment. If yes, a user-space buffer
'rxnfc'
is allocated through compat_alloc_user_space() and then the data in the
original buffer 'compat_rxnfc' is copied to 'rxnfc' through
copy_in_user(),
including the ioctl command. It is worth noting that after this copy,
there
is no check enforced on the copied ioctl command. That means it is
possible
that 'rxnfc->cmd' is different from 'ethcmd', because a malicious user
can
race to modify the ioctl command in 'compat_rxnfc' between these two
copies. Eventually, the ioctl command in 'rxnfc' will be used in
dev_ethtool(). This can cause undefined behavior of the kernel and
introduce potential security risk.

This patch avoids the above issue by rewriting 'rxnfc->cmd' using
'ethcmd'
after copy_in_user().

Signed-off-by: Wenwen Wang <redacted>

Assuming these issues are found with some kind of automated analysis, can you also add in your work flow to provide a Fixes: tag such that this could be backported to stable kernels?

If this is found by a tool is this something that is open source and somehow available? I would also make it clear that these issues are typically named time TOCTOU which might be clearer for people who review those patches.

Thanks!
-- 
Florian