From: Thomas Gleixner <[email protected]> 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 <[email protected]> Reviewed-by: Frederic Weisbecker <[email protected]> --- kernel/time/posix-cpu-timers.c | 66 +++++++++++++++++++---------------------- 1 file changed, 32 insertions(+), 34 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; /* @@ -64,50 +65,47 @@ 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(PROCESS) the task does not need to be - * the actual group leader. tsk->sighand gives - * access to the group's clock. - * - * Timers need the group leader because they take a - * reference on it and store the task pointer until the - * timer is destroyed. + * 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 it's own process, so spare - * the ptrace check below. + * 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 { + /* + * Process wide timers need the group leader because they + * take a reference on it and store the task pointer until + * the timer is destroyed. + */ + 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,
