diff options
author | Oleg Nesterov <oleg@redhat.com> | 2015-04-16 22:47:32 +0300 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2015-04-17 16:04:06 +0300 |
commit | 64a4096c5cdab377b6e1f44008ee8b2636db579d (patch) | |
tree | 5cb701ad9bd68e19f6da29b29c086215b0292b67 | |
parent | b72c186999e689cb0b055ab1c7b3cd8fffbeb5ed (diff) | |
download | linux-64a4096c5cdab377b6e1f44008ee8b2636db579d.tar.xz |
ptrace: ptrace_detach() can no longer race with SIGKILL
ptrace_detach() re-checks ->ptrace under tasklist lock and calls
release_task() if __ptrace_detach() returns true. This was needed because
the __TASK_TRACED tracee could be killed/untraced, and it could even pass
exit_notify() before we take tasklist_lock.
But this is no longer possible after 9899d11f6544 "ptrace: ensure
arch_ptrace/ptrace_request can never race with SIGKILL". We can turn
these checks into WARN_ON() and remove release_task().
While at it, document the setting of child->exit_code.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Pavel Labath <labath@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | kernel/ptrace.c | 19 |
1 files changed, 9 insertions, 10 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 9a34bd80a745..c8e0e050a36a 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -456,8 +456,6 @@ static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p) static int ptrace_detach(struct task_struct *child, unsigned int data) { - bool dead = false; - if (!valid_signal(data)) return -EIO; @@ -467,18 +465,19 @@ static int ptrace_detach(struct task_struct *child, unsigned int data) write_lock_irq(&tasklist_lock); /* - * This child can be already killed. Make sure de_thread() or - * our sub-thread doing do_wait() didn't do release_task() yet. + * We rely on ptrace_freeze_traced(). It can't be killed and + * untraced by another thread, it can't be a zombie. */ - if (child->ptrace) { - child->exit_code = data; - dead = __ptrace_detach(current, child); - } + WARN_ON(!child->ptrace || child->exit_state); + /* + * tasklist_lock avoids the race with wait_task_stopped(), see + * the comment in ptrace_resume(). + */ + child->exit_code = data; + __ptrace_detach(current, child); write_unlock_irq(&tasklist_lock); proc_ptrace_connector(child, PTRACE_DETACH); - if (unlikely(dead)) - release_task(child); return 0; } |