[PATCH 09/17] ptrace: Move setting/clearing ptrace_message into ptrace_stop

Eric W. Biederman
2022-01-03T21:34:02Z

Today ptrace_message is easy to overlook as it not a core part of
ptrace_stop. It has been overlooked so much that there are places
that set ptrace_message and don't clear it, and places that never set
it. So if you get an unlucky sequence of events the ptracer may be
able to read a ptrace_message that does not apply to the current
ptrace stop.

Move setting of ptrace_message into ptrace_stop so that it always gets
set before the stop, and always gets cleared after the stop. This
prevents non-sense from being reported to userspace and makes
ptrace_message more visible in the ptrace API so that kernel
developers can see it.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
include/linux/ptrace.h | 5 ++---
include/linux/tracehook.h | 6 ++----
kernel/signal.c | 19 +++++++++++--------
3 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 8aee2945ff08..06f27736c6f8 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -60,7 +60,7 @@ extern int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned
extern void ptrace_disable(struct task_struct *);
extern int ptrace_request(struct task_struct *child, long request,
unsigned long addr, unsigned long data);
-extern void ptrace_notify(int exit_code);
+extern void ptrace_notify(int exit_code, unsigned long message);
extern void __ptrace_link(struct task_struct *child,
struct task_struct *new_parent,
const struct cred *ptracer_cred);
@@ -155,8 +155,7 @@ static inline bool ptrace_event_enabled(struct task_struct *task, int event)
static inline void ptrace_event(int event, unsigned long message)
{
if (unlikely(ptrace_event_enabled(current, event))) {
- current->ptrace_message = message;
- ptrace_notify((event << 8) | SIGTRAP);
+ ptrace_notify((event << 8) | SIGTRAP, message);
} else if (event == PTRACE_EVENT_EXEC) {
/* legacy EXEC report via SIGTRAP */
if ((current->ptrace & (PT_PTRACED|PT_SEIZED)) == PT_PTRACED)
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 88c007ab5ebc..5e60af8a11fc 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -61,8 +61,7 @@ static inline int ptrace_report_syscall(unsigned long message)
if (!(ptrace & PT_PTRACED))
return 0;

- current->ptrace_message = message;
- ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
+ ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0), message);

/*
* this isn't the same as continuing with a signal, but it will do
@@ -74,7 +73,6 @@ static inline int ptrace_report_syscall(unsigned long message)
current->exit_code = 0;
}

- current->ptrace_message = 0;
return fatal_signal_pending(current);
}

@@ -143,7 +141,7 @@ static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
static inline void tracehook_signal_handler(int stepping)
{
if (stepping)
- ptrace_notify(SIGTRAP);
+ ptrace_notify(SIGTRAP, 0);
}

/**
diff --git a/kernel/signal.c b/kernel/signal.c
index 802acca0207b..75bb062d8534 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2197,7 +2197,8 @@ static void do_notify_parent_cldstop(struct task_struct *tsk,
* If we actually decide not to stop at all because the tracer
* is gone, we keep current->exit_code unless clear_code.
*/
-static void ptrace_stop(int exit_code, int why, int clear_code, kernel_siginfo_t *info)
+static void ptrace_stop(int exit_code, int why, int clear_code,
+ unsigned long message, kernel_siginfo_t *info)
__releases(&current->sighand->siglock)
__acquires(&current->sighand->siglock)
{
@@ -2243,6 +2244,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, kernel_siginfo_t
*/
smp_wmb();

+ current->ptrace_message = message;
current->last_siginfo = info;
current->exit_code = exit_code;

@@ -2321,6 +2323,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, kernel_siginfo_t
*/
spin_lock_irq(&current->sighand->siglock);
current->last_siginfo = NULL;
+ current->ptrace_message = 0;

/* LISTENING can be set only during STOP traps, clear it */
current->jobctl &= ~JOBCTL_LISTENING;
@@ -2333,7 +2336,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, kernel_siginfo_t
recalc_sigpending_tsk(current);
}

-static void ptrace_do_notify(int signr, int exit_code, int why)
+static void ptrace_do_notify(int signr, int exit_code, int why, unsigned long message)
{
kernel_siginfo_t info;

@@ -2344,17 +2347,17 @@ static void ptrace_do_notify(int signr, int exit_code, int why)
info.si_uid = from_kuid_munged(current_user_ns(), current_uid());

/* Let the debugger run. */
- ptrace_stop(exit_code, why, 1, &info);
+ ptrace_stop(exit_code, why, 1, message, &info);
}

-void ptrace_notify(int exit_code)
+void ptrace_notify(int exit_code, unsigned long message)
{
BUG_ON((exit_code & (0x7f | ~0xffff)) != SIGTRAP);
if (unlikely(current->task_works))
task_work_run();

spin_lock_irq(&current->sighand->siglock);
- ptrace_do_notify(SIGTRAP, exit_code, CLD_TRAPPED);
+ ptrace_do_notify(SIGTRAP, exit_code, CLD_TRAPPED, message);
spin_unlock_irq(&current->sighand->siglock);
}

@@ -2510,10 +2513,10 @@ static void do_jobctl_trap(void)
signr = SIGTRAP;
WARN_ON_ONCE(!signr);
ptrace_do_notify(signr, signr | (PTRACE_EVENT_STOP << 8),
- CLD_STOPPED);
+ CLD_STOPPED, 0);
} else {
WARN_ON_ONCE(!signr);
- ptrace_stop(signr, CLD_STOPPED, 0, NULL);
+ ptrace_stop(signr, CLD_STOPPED, 0, 0, NULL);
current->exit_code = 0;
}
}
@@ -2567,7 +2570,7 @@ static int ptrace_signal(int signr, kernel_siginfo_t *info, enum pid_type type)
* comment in dequeue_signal().
*/
current->jobctl |= JOBCTL_STOP_DEQUEUED;
- ptrace_stop(signr, CLD_TRAPPED, 0, info);
+ ptrace_stop(signr, CLD_TRAPPED, 0, 0, info);

/* We're back. Did the debugger cancel the sig? */
signr = current->exit_code;
--
2.29.2