The current implementation of PTRACE_KILL is buggy and has been for many years as it assumes it's target has stopped in ptrace_stop. At a quick skim it looks like this assumption has existed since ptrace support was added in linux v1.0.

While PTRACE_KILL has been deprecated we can not remove it as a quick search with google code search reveals many existing programs calling it.

When the ptracee is not stopped at ptrace_stop some fields would be set that are ignored except in ptrace_stop. Making the userspace visible behavior of PTRACE_KILL a noop in those case.

As the usual rules are not obeyed it is not clear what the consequences are of calling PTRACE_KILL on a running process. Presumably userspace does not do this as it achieves nothing.

Replace the implementation of PTRACE_KILL with a simple send_sig_info(SIGKILL) followed by a return 0. This changes the observable user space behavior only in that PTRACE_KILL on a process not stopped in ptrace_stop will also kill it. As that has always been the intent of the code this seems like a reasonable change.

Cc: stable@vger.kernel.org Reported-by: Al Viro viro@zeniv.linux.org.uk Suggested-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com --- arch/x86/kernel/step.c | 3 +-- kernel/ptrace.c | 5 ++--- 2 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c index 0f3c307b37b3..8e2b2552b5ee 100644 --- a/arch/x86/kernel/step.c +++ b/arch/x86/kernel/step.c @@ -180,8 +180,7 @@ void set_task_blockstep(struct task_struct *task, bool on) * * NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if * task is current or it can't be running, otherwise we can race - * with __switch_to_xtra(). We rely on ptrace_freeze_traced() but - * PTRACE_KILL is not safe. + * with __switch_to_xtra(). We rely on ptrace_freeze_traced(). */ local_irq_disable(); debugctl = get_debugctlmsr(); diff --git a/kernel/ptrace.c b/kernel/ptrace.c index da30dcd477a0..7105821595bc 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -1236,9 +1236,8 @@ int ptrace_request(struct task_struct *child, long request, return ptrace_resume(child, request, data);

case PTRACE_KILL: - if (child->exit_state) /* already dead */ - return 0; - return ptrace_resume(child, request, SIGKILL); + send_sig_info(SIGKILL, SEND_SIG_NOINFO, child); + return 0;

#ifdef CONFIG_HAVE_ARCH_TRACEHOOK case PTRACE_GETREGSET: