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ptrace: Don't change __state

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Stop playing with tsk->__state to remove TASK_WAKEKILL while a ptrace
command is executing.

Instead remove TASK_WAKEKILL from the definition of TASK_TRACED, and
implement a new jobctl flag TASK_PTRACE_FROZEN.  This new flag is set
in jobctl_freeze_task and cleared when ptrace_stop is awoken or in
jobctl_unfreeze_task (when ptrace_stop remains asleep).

In signal_wake_up add __TASK_TRACED to state along with TASK_WAKEKILL
when the wake up is for a fatal signal.  Skip adding __TASK_TRACED
when TASK_PTRACE_FROZEN is not set.  This has the same effect as
changing TASK_TRACED to __TASK_TRACED as all of the wake_ups that use
TASK_KILLABLE go through signal_wake_up.

Handle a ptrace_stop being called with a pending fatal signal.
Previously it would have been handled by schedule simply failing to
sleep.  As TASK_WAKEKILL is no longer part of TASK_TRACED schedule
will sleep with a fatal_signal_pending.   The code in signal_wake_up
guarantees that the code will be awaked by any fatal signal that
codes after TASK_TRACED is set.

Previously the __state value of __TASK_TRACED was changed to
TASK_RUNNING when woken up or back to TASK_TRACED when the code was
left in ptrace_stop.  Now when woken up ptrace_stop now clears
JOBCTL_PTRACE_FROZEN and when left sleeping ptrace_unfreezed_traced
clears JOBCTL_PTRACE_FROZEN.

Tested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lkml.kernel.org/r/20220505182645.497868-10-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2022-04-29 08:43:34 -05:00
parent 57b6de08b5
commit 2500ad1c7f
6 changed files with 21 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/sched.h
View File

@ -103,7 +103,7 @@ struct task_group;
/* Convenience macros for the sake of set_current_state: */
#define TASK_KILLABLE (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
#define TASK_STOPPED (TASK_WAKEKILL | __TASK_STOPPED)
#define TASK_TRACED (TASK_WAKEKILL | __TASK_TRACED)
#define TASK_TRACED __TASK_TRACED
#define TASK_IDLE (TASK_UNINTERRUPTIBLE | TASK_NOLOAD)

2
include/linux/sched/jobctl.h
View File

@ -19,6 +19,7 @@ struct task_struct;
#define JOBCTL_TRAPPING_BIT 21 /* switching to TRACED */
#define JOBCTL_LISTENING_BIT 22 /* ptracer is listening for events */
#define JOBCTL_TRAP_FREEZE_BIT 23 /* trap for cgroup freezer */
#define JOBCTL_PTRACE_FROZEN_BIT 24 /* frozen for ptrace */
#define JOBCTL_STOP_DEQUEUED (1UL << JOBCTL_STOP_DEQUEUED_BIT)
#define JOBCTL_STOP_PENDING (1UL << JOBCTL_STOP_PENDING_BIT)
@ -28,6 +29,7 @@ struct task_struct;
#define JOBCTL_TRAPPING (1UL << JOBCTL_TRAPPING_BIT)
#define JOBCTL_LISTENING (1UL << JOBCTL_LISTENING_BIT)
#define JOBCTL_TRAP_FREEZE (1UL << JOBCTL_TRAP_FREEZE_BIT)
#define JOBCTL_PTRACE_FROZEN (1UL << JOBCTL_PTRACE_FROZEN_BIT)
#define JOBCTL_TRAP_MASK (JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY)
#define JOBCTL_PENDING_MASK (JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK)

5
include/linux/sched/signal.h
View File

@ -435,9 +435,10 @@ extern void calculate_sigpending(void);
extern void signal_wake_up_state(struct task_struct *t, unsigned int state);
static inline void signal_wake_up(struct task_struct *t, bool resume)
static inline void signal_wake_up(struct task_struct *t, bool fatal)
{
signal_wake_up_state(t, resume ? TASK_WAKEKILL : 0);
fatal = fatal && !(t->jobctl & JOBCTL_PTRACE_FROZEN);
signal_wake_up_state(t, fatal ? TASK_WAKEKILL | __TASK_TRACED : 0);
}
static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume)
{

21
kernel/ptrace.c
View File

@ -197,7 +197,7 @@ static bool ptrace_freeze_traced(struct task_struct *task)
spin_lock_irq(&task->sighand->siglock);
if (task_is_traced(task) && !looks_like_a_spurious_pid(task) &&
!__fatal_signal_pending(task)) {
WRITE_ONCE(task->__state, __TASK_TRACED);
task->jobctl |= JOBCTL_PTRACE_FROZEN;
ret = true;
}
spin_unlock_irq(&task->sighand->siglock);
@ -207,23 +207,19 @@ static bool ptrace_freeze_traced(struct task_struct *task)
static void ptrace_unfreeze_traced(struct task_struct *task)
{
if (READ_ONCE(task->__state) != __TASK_TRACED)
return;
WARN_ON(!task->ptrace || task->parent != current);
unsigned long flags;
/*
* PTRACE_LISTEN can allow ptrace_trap_notify to wake us up remotely.
* Recheck state under the lock to close this race.
* The child may be awake and may have cleared
* JOBCTL_PTRACE_FROZEN (see ptrace_resume). The child will
* not set JOBCTL_PTRACE_FROZEN or enter __TASK_TRACED anew.
*/
spin_lock_irq(&task->sighand->siglock);
if (READ_ONCE(task->__state) == __TASK_TRACED) {
if (lock_task_sighand(task, &flags)) {
task->jobctl &= ~JOBCTL_PTRACE_FROZEN;
if (__fatal_signal_pending(task))
wake_up_state(task, __TASK_TRACED);
else
WRITE_ONCE(task->__state, TASK_TRACED);
unlock_task_sighand(task, &flags);
}
spin_unlock_irq(&task->sighand->siglock);
}
/**
@ -256,7 +252,6 @@ static int ptrace_check_attach(struct task_struct *child, bool ignore_state)
*/
read_lock(&tasklist_lock);
if (child->ptrace && child->parent == current) {
WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED);
/*
* child->sighand can't be NULL, release_task()
* does ptrace_unlink() before __exit_signal().

5
kernel/sched/core.c
View File

@ -6304,10 +6304,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
/*
* We must load prev->state once (task_struct::state is volatile), such
* that:
*
* - we form a control dependency vs deactivate_task() below.
* - ptrace_{,un}freeze_traced() can change ->state underneath us.
* that we form a control dependency vs deactivate_task() below.
*/
prev_state = READ_ONCE(prev->__state);
if (!(sched_mode & SM_MASK_PREEMPT) && prev_state) {

14
kernel/signal.c
View File

@ -2209,14 +2209,12 @@ static int ptrace_stop(int exit_code, int why, unsigned long message,
}
/*
* schedule() will not sleep if there is a pending signal that
* can awaken the task.
*
* After this point ptrace_signal_wake_up will clear TASK_TRACED
* if ptrace_unlink happens. Handle previous ptrace_unlinks
* here to prevent ptrace_stop sleeping in schedule.
* After this point ptrace_signal_wake_up or signal_wake_up
* will clear TASK_TRACED if ptrace_unlink happens or a fatal
* signal comes in. Handle previous ptrace_unlinks and fatal
* signals here to prevent ptrace_stop sleeping in schedule.
*/
if (!current->ptrace)
if (!current->ptrace || __fatal_signal_pending(current))
return exit_code;
set_special_state(TASK_TRACED);
@ -2305,7 +2303,7 @@ static int ptrace_stop(int exit_code, int why, unsigned long message,
current->exit_code = 0;
/* LISTENING can be set only during STOP traps, clear it */
current->jobctl &= ~JOBCTL_LISTENING;
current->jobctl &= ~(JOBCTL_LISTENING | JOBCTL_PTRACE_FROZEN);
/*
* Queued signals ignored us while we were stopped for tracing.