Commit a70c7b3c authored by Willem de Bruijn's avatar Willem de Bruijn Committed by Jakub Kicinski
Browse files

tun: revert fix group permission check 

This reverts commit 3ca459ea.

The blamed commit caused a regression when neither tun->owner nor
tun->group is set. This is intended to be allowed, but now requires
CAP_NET_ADMIN.

Discussion in the referenced thread pointed out that the original
issue that prompted this patch can be resolved in userspace.

The relaxed access control may also make a device accessible when it
previously wasn't, while existing users may depend on it to not be.

This is a clean pure git revert, except for fixing the indentation on
the gid_valid line that checkpatch correctly flagged.

Fixes: 3ca459ea ("tun: fix group permission check")
Link: https://lore.kernel.org/netdev/CAFqZXNtkCBT4f+PwyVRmQGoT3p1eVa01fCG_aNtpt6dakXncUg@mail.gmail.com/


Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
Cc: Ondrej Mosnacek <omosnace@redhat.com>
Cc: Stas Sergeev <stsp2@yandex.ru>
Link: https://patch.msgid.link/20250204161015.739430-1-willemdebruijn.kernel@gmail.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 02b71dc1

drivers/net/tun.c

+5 −9
Original line number Diff line number Diff line
@@ -574,18 +574,14 @@ static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb, 
	return ret;

}



static inline bool tun_capable(struct tun_struct *tun)

static inline bool tun_not_capable(struct tun_struct *tun)

{

	const struct cred *cred = current_cred();

	struct net *net = dev_net(tun->dev);



	if (ns_capable(net->user_ns, CAP_NET_ADMIN))

		return 1;

	if (uid_valid(tun->owner) && uid_eq(cred->euid, tun->owner))

		return 1;

	if (gid_valid(tun->group) && in_egroup_p(tun->group))

		return 1;

	return 0;

	return ((uid_valid(tun->owner) && !uid_eq(cred->euid, tun->owner)) ||

		(gid_valid(tun->group) && !in_egroup_p(tun->group))) &&

		!ns_capable(net->user_ns, CAP_NET_ADMIN);

}



static void tun_set_real_num_queues(struct tun_struct *tun)
@@ -2782,7 +2778,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr) 
		    !!(tun->flags & IFF_MULTI_QUEUE))

			return -EINVAL;



		if (!tun_capable(tun))

		if (tun_not_capable(tun))

			return -EPERM;

		err = security_tun_dev_open(tun->security);

		if (err < 0)