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: sta...@vger.kernel.org
Reported-by: Al Viro <v...@zeniv.linux.org.uk>
Suggested-by: Al Viro <v...@zeniv.linux.org.uk>
Signed-off-by: "Eric W. Biederman" <ebied...@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:
--
2.35.3
_______________________________________________
linux-um mailing list
linux-um@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-um
