The thread clock permissions are restricted to tasks of the same thread group, but that also prevents a ptracer from reading them. This is inconsistent vs. the process restrictions and unnecessary strict.
Relax it to ptrace permissions in the same way as process permissions are handled. Signed-off-by: Thomas Gleixner <t...@linutronix.de> --- kernel/time/posix-cpu-timers.c | 56 +++++++++++++++++++++-------------------- 1 file changed, 29 insertions(+), 27 deletions(-) --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -51,6 +51,7 @@ void update_rlimit_cpu(struct task_struc static struct task_struct *lookup_task(const pid_t pid, bool thread, bool gettime) { + unsigned int mode = PTRACE_MODE_ATTACH_REALCREDS; struct task_struct *p; /* @@ -64,44 +65,45 @@ static struct task_struct *lookup_task(c if (!p) return p; - if (thread) - return same_thread_group(p, current) ? p : NULL; - if (gettime) { /* * For clock_gettime() the task does not need to be the * actual group leader. tsk->sighand gives access to the - * group's clock. current can obviously access itself, so - * spare the ptrace check below. + * group's clock. + * + * The trivial case is that p is current or in the same + * thread group, i.e. sharing p->signal. Spare the ptrace + * check in that case. */ - if (p == current) + if (same_thread_group(p, current)) return p; - if (!thread_group_leader(p)) - return NULL; + mode = PTRACE_MODE_READ_REALCREDS; - if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) - return NULL; - return p; - } + } else if (thread) { + /* + * Timer is going to be attached to a thread. If p is + * current or in the same thread group, granted. + */ + if (same_thread_group(p, current)) + return p; - /* - * For processes require that p is group leader. - */ - if (!has_group_leader_pid(p)) - return NULL; + } else { + /* + * For processes require that p is group leader. + */ + if (!has_group_leader_pid(p)) + return NULL; - /* - * Avoid the ptrace overhead when this is current's process - */ - if (same_thread_group(p, current)) - return p; + /* + * Avoid the ptrace overhead when this is current's process + */ + if (same_thread_group(p, current)) + return p; + } - /* - * Creating timers on processes which cannot be ptraced is not - * permitted: - */ - return ptrace_may_access(p, PTRACE_MODE_ATTACH_REALCREDS) ? p : NULL; + /* Decide based on the ptrace permissions. */ + return ptrace_may_access(p, mode) ? p : NULL; } static struct task_struct *__get_task_for_clock(const clockid_t clock,