5.4-stable review patch. If anyone has any objections, please let me know.
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From: Willem de Bruijn willemb@google.com
[ 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_aNtpt6da... 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... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 87cc7d778c3cf..1a6b4cdc3bd5d 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -636,18 +636,14 @@ 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) @@ -2842,7 +2838,7 @@ 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)