5.4-stable review patch. If anyone has any objections, please let me know.
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From: Stas Sergeev stsp2@yandex.ru
[ 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@yandex.ru Reviewed-by: Willem de Bruijn willemb@google.com Acked-by: Jason Wang jasowang@redhat.com Link: https://patch.msgid.link/20241205073614.294773-1-stsp2@yandex.ru Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/tun.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 0adce9bf7a1e5..87cc7d778c3cf 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -636,14 +636,18 @@ 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) @@ -2838,7 +2842,7 @@ 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)