Commit 992fb6e1 authored Dec 17, 2012 by Oleg Nesterov Committed by Linus Torvalds Dec 17, 2012

ptrace: introduce PTRACE_O_EXITKILL



Ptrace jailers want to be sure that the tracee can never escape
from the control. However if the tracer dies unexpectedly the
tracee continues to run in potentially unsafe mode.

Add the new ptrace option PTRACE_O_EXITKILL. If the tracer exits
it sends SIGKILL to every tracee which has this bit set.

Note that the new option is not equal to the last-option << 1.  Because
currently all options have an event, and the new one starts the eventless
group.  It uses the random 20 bit, so we have the room for 12 more events,
but we can also add the new eventless options below this one.

Suggested by Amnon Shiloh.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Amnon Shiloh <u3557@miso.sublimeip.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Chris Evans <scarybeasts@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 462e4711

include/linux/ptrace.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -32,6 +32,8 @@
		#define PT_TRACE_EXIT PT_EVENT_FLAG(PTRACE_EVENT_EXIT)
		#define PT_TRACE_SECCOMP PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP)

		#define PT_EXITKILL (PTRACE_O_EXITKILL << PT_OPT_FLAG_SHIFT)

		/* single stepping state bits (used on ARM and PA-RISC) */
		#define PT_SINGLESTEP_BIT 31
		#define PT_SINGLESTEP (1<<PT_SINGLESTEP_BIT)

include/uapi/linux/ptrace.h

+4 −1

Original line number	Diff line number	Diff line
		@@ -73,7 +73,10 @@
		#define PTRACE_O_TRACEEXIT (1 << PTRACE_EVENT_EXIT)
		#define PTRACE_O_TRACESECCOMP (1 << PTRACE_EVENT_SECCOMP)

		#define PTRACE_O_MASK 0x000000ff
		/* eventless options */
		#define PTRACE_O_EXITKILL (1 << 20)

		#define PTRACE_O_MASK (0x000000ff \| PTRACE_O_EXITKILL)

		#include <asm/ptrace.h>

kernel/ptrace.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -457,6 +457,9 @@ void exit_ptrace(struct task_struct *tracer)
		return;

		list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) {
		if (unlikely(p->ptrace & PT_EXITKILL))
		send_sig_info(SIGKILL, SEND_SIG_FORCED, p);

		if (__ptrace_detach(tracer, p))
		list_add(&p->ptrace_entry, &ptrace_dead);
		}

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