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Subject[Question] Should `CAP_NET_ADMIN` be needed when opening `/dev/ppp`?
Date
Hi, all.


I’ve recently met some problems when trying to create a pppoe network link
inside a unprivileged container. There is a uid namespace which maps root
inside to a normal user outside. There is also a separate net namespace in the
container. I create a dev node inside the container and set right
permission.

However, `/dev/ppp` cannot get opened since the mapped normal user does not
have `CAP_NET_ADMIN`. The related code is in `drivers/net/ppp/ppp_generic.c`:
`int ppp_open()`

```
static int ppp_open(struct inode *inode, struct file *file)
{
/*
* This could (should?) be enforced by the permissions on /dev/ppp.
*/
if (!capable(CAP_NET_ADMIN))
return -EPERM;
return 0;
}
```

I wonder why CAP_NET_ADMIN is needed here, rather than leaving it to the
permission of the device node. If there is no need, I suggest that the
CAP_NET_ADMIN check be removed.

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