[PATCH net v2] tun: revert fix group permission check
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: 2025-02-04 16:10:22
Subsystem:
networking drivers, the rest, tun/tap driver · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Willem de Bruijn, Jason Wang
From: Willem de Bruijn <willemb@google.com>
This reverts commit 3ca459eaba1bf96a8c7878de84fa8872259a01e3.
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: 3ca459eaba1b ("tun: fix group permission check")
Link: https://lore.kernel.org/netdev/CAFqZXNtkCBT4f+PwyVRmQGoT3p1eVa01fCG_aNtpt6dakXncUg@mail.gmail.com/ (local)
Signed-off-by: Willem de Bruijn <willemb@google.com>
Cc: Ondrej Mosnacek <omosnace@redhat.com>
Cc: Stas Sergeev <redacted>
---
drivers/net/tun.c | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 28624cca91f8..acf96f262488 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c@@ -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)
--
2.48.1.362.g079036d154-goog