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[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>
This commit is contained in:
Oleg Nesterov 2005-11-07 21:12:43 +03:00 committed by Linus Torvalds
parent a52e8381c4
commit 329f7dba5f
1 changed files with 7 additions and 3 deletions
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10
fs/exec.c
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@ -590,6 +590,7 @@ static inline int de_thread(struct task_struct *tsk)
struct signal_struct *sig = tsk->signal; struct signal_struct *sig = tsk->signal;
struct sighand_struct *newsighand, *oldsighand = tsk->sighand; struct sighand_struct *newsighand, *oldsighand = tsk->sighand;
spinlock_t *lock = &oldsighand->siglock; spinlock_t *lock = &oldsighand->siglock;
struct task_struct *leader = NULL;
int count; int count;
/* /*
@ -665,7 +666,7 @@ static inline int de_thread(struct task_struct *tsk)
* and to assume its PID: * and to assume its PID:
*/ */
if (!thread_group_leader(current)) { if (!thread_group_leader(current)) {
struct task_struct *leader = current->group_leader, *parent; struct task_struct *parent;
struct dentry *proc_dentry1, *proc_dentry2; struct dentry *proc_dentry1, *proc_dentry2;
unsigned long exit_state, ptrace; 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 * It should already be zombie at this point, most
* of the time. * of the time.
*/ */
leader = current->group_leader;
while (leader->exit_state != EXIT_ZOMBIE) while (leader->exit_state != EXIT_ZOMBIE)
yield(); yield();
@ -733,7 +735,6 @@ static inline int de_thread(struct task_struct *tsk)
proc_pid_flush(proc_dentry2); proc_pid_flush(proc_dentry2);
BUG_ON(exit_state != EXIT_ZOMBIE); 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; sig->flags = 0;
no_thread_group: no_thread_group:
BUG_ON(atomic_read(&sig->count) != 1);
exit_itimers(sig); exit_itimers(sig);
if (leader)
release_task(leader);
BUG_ON(atomic_read(&sig->count) != 1);
if (atomic_read(&oldsighand->count) == 1) { if (atomic_read(&oldsighand->count) == 1) {
/* /*