6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Willem de Bruijn <willemb@xxxxxxxxxx>
[ Upstream commit a70c7b3cbc0688016810bb2e0b9b8a0d6a530045 ]
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@xxxxxxxxxxxxxx/
Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Cc: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
Cc: Stas Sergeev <stsp2@xxxxxxxxx>
Link: https://patch.msgid.link/20250204161015.739430-1-willemdebruijn.kernel@xxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 6c24a9ce6c155..fae1a0ab36bdf 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)
--
2.39.5
