On Fri, Dec 13, 2024 at 3:09 PM Paul Moore [off-list ref] wrote:

On Fri, Dec 13, 2024 at 11:40 AM Mikhail Ivanov
[off-list ref] wrote:

quoted

On 12/13/2024 6:46 PM, Stephen Smalley wrote:

quoted

On Fri, Dec 13, 2024 at 5:57 AM Mikhail Ivanov
[off-list ref] wrote:

quoted

On 12/12/2024 8:50 PM, Mickaël Salaün wrote:

quoted

This looks good be there are other places using sk->sk_family that
should also be fixed.

Thanks for checking this!

For selinux this should be enough, I haven't found any other places
where sk->sk_family could be read from an IPv6 socket without locking.

I also would like to prepare such fix for other LSMs (apparmor, smack,
tomoyo) (in separate patches).

I'm wondering about the implications for SELinux beyond just
sk->sk_family access, e.g. SELinux maps the (family, type, protocol)
triple to a security class at socket creation time via
socket_type_to_security_class() and caches the security class in the
inode_security_struct and sk_security_struct for later use.

IPv6 and IPv4 TCP sockets are mapped to the same SECCLASS_TCP_SOCKET
security class. AFAICS there is no other places that can be affected by
the IPV6_ADDFORM transformation.

Yes, thankfully we don't really encode the IP address family in any of
the SELinux object classes so that shouldn't be an issue.  I also
don't think we have to worry about the per-packet labeling protocols
as it's too late in the communication to change the socket's
associated packet labeling, it's either working or it isn't; we should
handle the mapped IPv4 address already.

I am a little concerned about bind being the only place where we have
to worry about accessing sk_family while the socket isn't locked.  As
an example, I'm a little concerned about the netfilter code paths; I
haven't chased them down, but my guess is that the associated
socket/sock isn't locked in those cases (in the relevant output and
postroute cases, forward should be a non-issue).

How bad is the performance impact of READ_ONCE()?  In other words, how
stupid would it be to simply do all of our sock->sk_family lookups
using READ_ONCE()?

I could be wrong, but I don't think there is any overhead except on Dec Alpha.