[patch 66/87] ptrace: fix possible zombie leak on PTRACE_DETACH

From: Greg KH
Date: Tue Jun 09 2009 - 06:33:24 EST

2.6.29-stable review patch. If anyone has any objections, please let us know.


From: Oleg Nesterov <oleg@xxxxxxxxxx>

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

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Jerome Marchand <jmarchan@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Tested-by: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

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);
--- 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
clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);

- /* protect against de_thread()->release_task() */
+ /* 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)

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

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