Commit 329f7dba authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

[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: default avatarOleg Nesterov <oleg@tv-sign.ru>
Acked-by: default avatarChris Wright <chrisw@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent a52e8381
......@@ -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) {
/*
......
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