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 <[email protected]>
---
net/socket.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/net/socket.c b/net/socket.c
index 01f3f8f..c5f969c 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2879,6 +2879,8 @@ static int ethtool_ioctl(struct net *net, struct compat_ifreq __user *ifr32)
copy_in_user(&rxnfc->rule_cnt, &compat_rxnfc->rule_cnt,
sizeof(rxnfc->rule_cnt)))
return -EFAULT;
+
+ rxnfc->cmd = ethcmd;
}
ret = dev_ioctl(net, SIOCETHTOOL, &ifr, NULL);
--
2.7.4
Hi Wenwen,
On October 20, 2018 8:58:10 AM PDT, Wenwen Wang <[email protected]> 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 <[email protected]>
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
Hi Florian,
Thanks for your response. The bug is found with the assistance of a
research prototype, which is now not available to the public.
Yes, this is a kind of time-of-check-to-time-of-use (TOCTTOU) bug.
BTW, could you please confirm this bug? Thanks!
Wenwen
On Sat, Oct 20, 2018 at 10:21 PM Florian Fainelli <[email protected]> wrote:
>
> Hi Wenwen,
>
> On October 20, 2018 8:58:10 AM PDT, Wenwen Wang <[email protected]> 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 <[email protected]>
>
> 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