From: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> commit 6a2d90ba027adba528509ffa27097cffd3879257 upstream. 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@xxxxxxxxxxxxxxx Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Suggested-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Tested-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Oleg Nesterov <oleg@xxxxxxxxxx> Link: https://lkml.kernel.org/r/20220505182645.497868-7-ebiederm@xxxxxxxxxxxx Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/step.c | 3 +-- kernel/ptrace.c | 5 ++--- 2 files changed, 3 insertions(+), 5 deletions(-) --- a/arch/x86/kernel/step.c +++ b/arch/x86/kernel/step.c @@ -175,8 +175,7 @@ void set_task_blockstep(struct task_stru * * 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(); --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -1127,9 +1127,8 @@ int ptrace_request(struct task_struct *c 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:
