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Subject[patch 66/87] ptrace: fix possible zombie leak on PTRACE_DETACH
2.6.29-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Oleg Nesterov <oleg@redhat.com>

commit 4576145c1ecdaaea9ef8976a48335206aa1ebf91 upstream.

When ptrace_detach() takes tasklist, the tracee can be SIGKILL'ed. If it
has already passed exit_notify() we can leak a zombie, because a) ptracing
disables the auto-reaping logic, and b) ->real_parent was not notified
about the child's death.

ptrace_detach() should follow the ptrace_exit's logic, change the code
accordingly.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Tested-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
include/linux/ptrace.h | 1 +
kernel/ptrace.c | 9 +++++++--
2 files changed, 8 insertions(+), 2 deletions(-)
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -94,6 +94,7 @@ extern void ptrace_notify(int exit_code)
extern void __ptrace_link(struct task_struct *child,
struct task_struct *new_parent);
extern void __ptrace_unlink(struct task_struct *child);
+extern int __ptrace_detach(struct task_struct *tracer, struct task_struct *p);
extern void ptrace_fork(struct task_struct *task, unsigned long clone_flags);
#define PTRACE_MODE_READ 1
#define PTRACE_MODE_ATTACH 2
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -237,6 +237,8 @@ out:

int ptrace_detach(struct task_struct *child, unsigned int data)
{
+ int dead = 0;
+
if (!valid_signal(data))
return -EIO;

@@ -244,18 +246,21 @@ int ptrace_detach(struct task_struct *ch
ptrace_disable(child);
clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);

- /* protect against de_thread()->release_task() */
write_lock_irq(&tasklist_lock);
+ /* protect against de_thread()->release_task() */
if (child->ptrace) {
child->exit_code = data;

- __ptrace_unlink(child);
+ dead = __ptrace_detach(current, child);

if (!child->exit_state)
wake_up_process(child);
}
write_unlock_irq(&tasklist_lock);

+ if (unlikely(dead))
+ release_task(child);
+
return 0;
}




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