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tun: revert fix group permission check

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[ 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@mail.gmail.com/
Signed-off-by: Willem 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: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Willem de Bruijn
2025-02-04 11:10:06 -05:00
committed by Greg Kroah-Hartman
parent 6312555249
commit e36364d5d4
1 changed files with 5 additions and 9 deletions
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14
drivers/net/tun.c
View File

@@ -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)