From 329f7dba5f7dc3bc9a30ad00cf373d2e83115aa1 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@tv-sign.ru>
Date: Mon, 7 Nov 2005 21:12:43 +0300
Subject: [PATCH] [PATCH] fix de_thread() vs send_group_sigqueue() race
When non-leader thread does exec, de_thread calls release_task(leader) before
calling exit_itimers(). If local timer interrupt happens in between, it can
oops in send_group_sigqueue() while taking ->sighand->siglock == NULL.
However, we can't change send_group_sigqueue() to check p->signal != NULL,
because sys_timer_create() does get_task_struct() only in SIGEV_THREAD_ID
case. So it is possible that this task_struct was already freed and we can't
trust p->signal.
This patch changes de_thread() so that leader released after exit_itimers()
call.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Chris Wright <chrisw@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---
fs/exec.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index cd6c574557dc..5a4e3acc2e9f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -590,6 +590,7 @@ static inline int de_thread(struct task_struct *tsk)
struct signal_struct *sig = tsk->signal;
struct sighand_struct *newsighand, *oldsighand = tsk->sighand;
spinlock_t *lock = &oldsighand->siglock;
+ struct task_struct *leader = NULL;
int count;
/*
@@ -665,7 +666,7 @@ static inline int de_thread(struct task_struct *tsk)
* and to assume its PID:
*/
if (!thread_group_leader(current)) {
- struct task_struct *leader = current->group_leader, *parent;
+ struct task_struct *parent;
struct dentry *proc_dentry1, *proc_dentry2;
unsigned long exit_state, ptrace;
@@ -674,6 +675,7 @@ static inline int de_thread(struct task_struct *tsk)
* It should already be zombie at this point, most
* of the time.
*/
+ leader = current->group_leader;
while (leader->exit_state != EXIT_ZOMBIE)
yield();
@@ -733,7 +735,6 @@ static inline int de_thread(struct task_struct *tsk)
proc_pid_flush(proc_dentry2);
BUG_ON(exit_state != EXIT_ZOMBIE);
- release_task(leader);
}
/*
@@ -743,8 +744,11 @@ static inline int de_thread(struct task_struct *tsk)
sig->flags = 0;
no_thread_group:
- BUG_ON(atomic_read(&sig->count) != 1);
exit_itimers(sig);
+ if (leader)
+ release_task(leader);
+
+ BUG_ON(atomic_read(&sig->count) != 1);
if (atomic_read(&oldsighand->count) == 1) {
/*
--
2.20.1