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Subject[PATCH 18/19] ptrace: add JOBCTL_BLOCK_NOTIFY
Date
For to-be-added notification retraps, other tasks need to be able to
tell whether ptrace request is currently in progress while tracee is
in STOP trap. This patch adds JOBCTL_BLOCK_NOTIFY which is set on
ptrace_check_attach() if the request requires tracee to be trapped and
it's trapped for STOP, and cleared when ptrace syscall finishes.

This flag isn't used yet.

-v2: ptrace_put_task_struct() reorganized per Oleg's comment.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/ptrace.h | 2 +
include/linux/sched.h | 1 +
kernel/ptrace.c | 54 ++++++++++++++++++++++++++++++++++++++++++-----
3 files changed, 51 insertions(+), 6 deletions(-)

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 1e84960..2e39f81 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -73,6 +73,8 @@
#define PTRACE_EVENT_EXIT 6
#define PTRACE_EVENT_STOP 7

+#define PTRACE_STOP_SI_CODE (__SI_TRAP | SIGTRAP | PTRACE_EVENT_STOP << 8)
+
/* flags in siginfo.si_pt_flags from PTRACE_GETSIGINFO */
#define PTRACE_SI_STOPPED 0x00000001 /* tracee is job control stopped */

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9a0e1bc..9298f97 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1801,6 +1801,7 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
#define JOBCTL_STOP_CONSUME (1 << 18) /* consume group stop count */
#define JOBCTL_TRAP_STOP (1 << 19) /* trap for STOP */
#define JOBCTL_TRAPPING (1 << 21) /* switching to TRACED */
+#define JOBCTL_BLOCK_NOTIFY (1 << 22) /* block NOTIFY re-traps */

#define JOBCTL_TRAP_MASK JOBCTL_TRAP_STOP
#define JOBCTL_PENDING_MASK (JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK)
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index a9b3c67..1982d7a 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -128,11 +128,13 @@ void __ptrace_unlink(struct task_struct *child)
spin_lock(&child->sighand->siglock);

/*
- * Clear all pending traps and TRAPPING. TRAPPING should be
- * cleared regardless of JOBCTL_STOP_PENDING. Do it explicitly.
+ * Clear all pending traps, TRAPPING and BLOCK_NOTIFY. TRAPPING
+ * should be cleared regardless of JOBCTL_STOP_PENDING. Do it
+ * explicitly.
*/
task_clear_jobctl_pending(child, JOBCTL_TRAP_MASK);
task_clear_jobctl_trapping(child);
+ child->jobctl &= ~JOBCTL_BLOCK_NOTIFY;

/*
* Reinstate JOBCTL_STOP_PENDING if group stop is in effect and
@@ -191,10 +193,24 @@ int ptrace_check_attach(struct task_struct *child, bool ignore_state)
*/
spin_lock_irq(&child->sighand->siglock);
WARN_ON_ONCE(task_is_stopped(child));
- if (task_is_traced(child) || ignore_state)
+
+ if (ignore_state) {
+ ret = 0;
+ } else if (task_is_traced(child)) {
+ siginfo_t *si = child->last_siginfo;
+
+ /*
+ * If STOP trapped, ptrace notification may cause
+ * re-traps, which we don't want while ptrace
+ * request is in progress. Block notification.
+ */
+ if (si && si->si_code == PTRACE_STOP_SI_CODE)
+ child->jobctl |= JOBCTL_BLOCK_NOTIFY;
ret = 0;
- else if (ptrace_wait_trapping(child))
+ } else if (ptrace_wait_trapping(child)) {
return restart_syscall();
+ }
+
spin_unlock_irq(&child->sighand->siglock);
}
read_unlock(&tasklist_lock);
@@ -887,6 +903,32 @@ static struct task_struct *ptrace_get_task_struct(pid_t pid)
#define arch_ptrace_attach(child) do { } while (0)
#endif

+/**
+ * ptrace_put_task_struct - ptrace request processing done, put child
+ * @child: child task struct to put
+ *
+ * ptrace request processing for @child is finished. Clean up and put
+ * @child. This function clears %JOBCTL_BLOCK_NOTIFY which can be set by
+ * ptrace_check_attach(). @child might not be being ptraced by %current.
+ */
+static void ptrace_put_task_struct(struct task_struct *child)
+{
+ unsigned long flags;
+
+ if (!(child->jobctl & JOBCTL_BLOCK_NOTIFY))
+ goto out_put;
+
+ if (unlikely(!(child->ptrace & PT_PTRACED) || child->parent != current))
+ goto out_put;
+
+ if (likely(lock_task_sighand(child, &flags))) {
+ child->jobctl &= ~JOBCTL_BLOCK_NOTIFY;
+ unlock_task_sighand(child, &flags);
+ }
+out_put:
+ put_task_struct(child);
+}
+
SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
unsigned long, data)
{
@@ -925,7 +967,7 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
ret = arch_ptrace(child, request, addr, data);

out_put_task_struct:
- put_task_struct(child);
+ ptrace_put_task_struct(child);
out:
return ret;
}
@@ -1066,7 +1108,7 @@ asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid,
ret = compat_arch_ptrace(child, request, addr, data);

out_put_task_struct:
- put_task_struct(child);
+ ptrace_put_task_struct(child);
out:
return ret;
}
--
1.7.1


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