"Serge E. Hallyn" <serge@xxxxxxxxxx> writes:
> Changelog:
> Dec 8: Fixed bug in my check_kill_permission pointed out by
> Eric Biederman.
>
> To test:
> 1. Test killing tasks as usual. No change.
> 2. Clone a new user namespace without a new pidns.
> a. You CAN kill -CONT tasks in your thread group but outside
> your user ns.
> b. You can NOT otherwise kill tasks outside your user_ns.
> c. Inside your new userns, signal semantics are as normal
> with respect to userids, CAP_KILL, and thread groups.
>
> Signed-off-by: Serge E. Hallyn <serge.hallyn@xxxxxxxxxxxxx>
> ---
> kernel/signal.c | 27 ++++++++++++++++++++++-----
> 1 files changed, 22 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 4e3cff1..677025c 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -635,6 +635,27 @@ static inline bool si_fromuser(const struct siginfo *info)
> (!is_si_special(info) && SI_FROMUSER(info));
> }
>
> +static inline int kill_ok_by_cred(struct cred *cred, struct cred *tcred)
> +{
Nit: You should just pass in the target task here.
Making it abundantly clear where current and tcred come from.
ns_capable implicitly uses current which is a little surprising
when everything else is being passed in, but makes perfect sense
in this context.
> + if (cred->user->user_ns != tcred->user->user_ns) {
> + /* userids are not equivalent - either you have the
> + capability to the target user ns or you don't */
> + if (ns_capable(tcred->user->user_ns, CAP_KILL))
> + return 1;
> + return 0;
> + }
> +
> + /* same user namespace - usual credentials checks apply */
> + if ((cred->euid ^ tcred->suid) &&
> + (cred->euid ^ tcred->uid) &&
> + (cred->uid ^ tcred->suid) &&
> + (cred->uid ^ tcred->uid) &&
> + !ns_capable(tcred->user->user_ns, CAP_KILL))
> + return 0;
> +
> + return 1;
> +}
> +
> /*
> * Bad permissions for sending the signal
> * - the caller must hold the RCU read lock
> @@ -659,11 +680,7 @@ static int check_kill_permission(int sig, struct siginfo *info,
> cred = current_cred();
> tcred = __task_cred(t);
> if (!same_thread_group(current, t) &&
> - (cred->euid ^ tcred->suid) &&
> - (cred->euid ^ tcred->uid) &&
> - (cred->uid ^ tcred->suid) &&
> - (cred->uid ^ tcred->uid) &&
> - !capable(CAP_KILL)) {
> + !kill_ok_by_cred(cred, tcred)) {
> switch (sig) {
> case SIGCONT:
> sid = task_session(t);
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