"Serge E. Hallyn" <serge@xxxxxxxxxx> writes:
> Quoting Eric W. Biederman (ebiederm@xxxxxxxxxxxx):
>> "Serge E. Hallyn" <serge@xxxxxxxxxx> writes:
>>
>> > Quoting Eric W. Biederman (ebiederm@xxxxxxxxxxxx):
>> >> > --- a/kernel/signal.c
>> >> > +++ b/kernel/signal.c
>> >> > @@ -659,11 +686,7 @@ static int check_kill_permission(int sig, struct siginfo *info,
>> >> > cred = current_cred();
>> >> > tcred = __task_cred(t);
>> >> Nit pick you don't need to compute cred and tcred here now.
>> >
>> > Just to make sure I understand right: you mean wait until after the
>> > same_thread_group() check to save calculation in that case, right?
>>
>> I mean cred and tcred are only use in kill_ok_by_cred.
>> So we can eliminate those two variables from check_kill_permission.
>
> Thanks for the review. Here is an updated version.
This one looks good.
Reviewed-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
>
> Subject: [PATCH 4/5] allow killing tasks in your own or child userns
>
> Changelog:
> Dec 8: Fixed bug in my check_kill_permission pointed out by
> Eric Biederman.
> Dec 13: Apply Eric's suggestion to pass target task into kill_ok_by_cred()
> for clarity
> Dec 31: address comment by Eric Biederman:
> don't need cred/tcred in check_kill_permission.
>
> Signed-off-by: Serge E. Hallyn <serge.hallyn@xxxxxxxxxxxxx>
> ---
> kernel/signal.c | 36 ++++++++++++++++++++++++++++--------
> 1 files changed, 28 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 4e3cff1..d890c99 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -636,13 +636,39 @@ static inline bool si_fromuser(const struct siginfo *info)
> }
>
> /*
> + * called with RCU read lock from check_kill_permission()
> + */
> +static inline int kill_ok_by_cred(struct task_struct *t)
> +{
> + struct cred *cred = current_cred();
> + struct cred *tcred = __task_cred(t);
> +
> + 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
> */
> static int check_kill_permission(int sig, struct siginfo *info,
> struct task_struct *t)
> {
> - const struct cred *cred, *tcred;
> struct pid *sid;
> int error;
>
> @@ -656,14 +682,8 @@ static int check_kill_permission(int sig, struct siginfo *info,
> if (error)
> return error;
>
> - 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(t)) {
> switch (sig) {
> case SIGCONT:
> sid = task_session(t);
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