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SubjectRe: [PATCH 7/8] user ns: handle file sigio
"Serge E. Hallyn" <> writes:

> From: Serge E. Hallyn <>
> Subject: [PATCH 7/8] user ns: handle file sigio
> A process in one user namespace could set a fowner and sigio on a file in a
> shared vfsmount, ending up killing a task in another user namespace.
> Prevent this by adding a user namespace pointer to the fown_struct, and
> enforcing that a process causing a signal to be sent be in the same
> user namespace as the file owner.

> @@ -455,6 +460,9 @@ static const long band_table[NSIGPOLL] =
> static inline int sigio_perm(struct task_struct *p,
> struct fown_struct *fown, int sig)
> {
> + if (fown->user_ns != init_task.nsproxy->user_ns &&
> + fown->user_ns != p->nsproxy->user_ns)
> + return 0;

Why is the initial user namespace being treated specially here?
Especially when you start considering nested containers special treatment
like this is semantically a real problem, to maintain.

If we need to I can see doing something special if the process setting
fown has CAP_KILL and bypassing the security checks that way, but
hard coding rules like that when it doesn't appear we have any
experience to indicate we need the extra functionality looks

> return (((fown->euid == 0) ||
> (fown->euid == p->suid) || (fown->euid == p->uid) ||
> (fown->uid == p->suid) || (fown->uid == p->uid)) &&

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