This is a note to let you know that I've just added the patch titled
tun: fix group permission check
to the 6.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tun-fix-group-permission-check.patch
and it can be found in the queue-6.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 0e5a10324d3824c5ff9fd0bcefd0b89141f5bd8a
Author: Stas Sergeev <stsp2@xxxxxxxxx>
Date: Thu Dec 5 10:36:14 2024 +0300
tun: fix group permission check
[ Upstream commit 3ca459eaba1bf96a8c7878de84fa8872259a01e3 ]
Currently tun checks the group permission even if the user have matched.
Besides going against the usual permission semantic, this has a
very interesting implication: if the tun group is not among the
supplementary groups of the tun user, then effectively no one can
access the tun device. CAP_SYS_ADMIN still can, but its the same as
not setting the tun ownership.
This patch relaxes the group checking so that either the user match
or the group match is enough. This avoids the situation when no one
can access the device even though the ownership is properly set.
Also I simplified the logic by removing the redundant inversions:
tun_not_capable() --> !tun_capable()
Signed-off-by: Stas Sergeev <stsp2@xxxxxxxxx>
Reviewed-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Link: https://patch.msgid.link/20241205073614.294773-1-stsp2@xxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 6fc60950100c7..6c24a9ce6c155 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -574,14 +574,18 @@ static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,
return ret;
}
-static inline bool tun_not_capable(struct tun_struct *tun)
+static inline bool tun_capable(struct tun_struct *tun)
{
const struct cred *cred = current_cred();
struct net *net = dev_net(tun->dev);
- 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);
+ 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;
}
static void tun_set_real_num_queues(struct tun_struct *tun)
@@ -2778,7 +2782,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
!!(tun->flags & IFF_MULTI_QUEUE))
return -EINVAL;
- if (tun_not_capable(tun))
+ if (!tun_capable(tun))
return -EPERM;
err = security_tun_dev_open(tun->security);
if (err < 0)
