This makes the code clearer and makes it easier to implement a mutex that is not taken over any locations that may block indefinitely waiting for userspace.
Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com Reviewed-by: Bernd Edlinger bernd.edlinger@hotmail.de Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Christian Brauner christian.brauner@ubuntu.com Reviewed-by: Kirill Tkhai ktkhai@virtuozzo.com --- fs/exec.c | 39 ++++++++++++++++++++++++++------------- 1 file changed, 26 insertions(+), 13 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c index c3f3479..ff74b9a 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1194,6 +1194,23 @@ static int de_thread(struct task_struct *tsk) flush_itimer_signals(); #endif
+ BUG_ON(!thread_group_leader(tsk)); + return 0; + +killed: + /* protects against exit_notify() and __exit_signal() */ + read_lock(&tasklist_lock); + sig->group_exit_task = NULL; + sig->notify_count = 0; + read_unlock(&tasklist_lock); + return -EAGAIN; +} + + +static int unshare_sighand(struct task_struct *me) +{ + struct sighand_struct *oldsighand = me->sighand; + if (refcount_read(&oldsighand->count) != 1) { struct sighand_struct *newsighand; /* @@ -1210,23 +1227,13 @@ static int de_thread(struct task_struct *tsk)
write_lock_irq(&tasklist_lock); spin_lock(&oldsighand->siglock); - rcu_assign_pointer(tsk->sighand, newsighand); + rcu_assign_pointer(me->sighand, newsighand); spin_unlock(&oldsighand->siglock); write_unlock_irq(&tasklist_lock);
__cleanup_sighand(oldsighand); } - - BUG_ON(!thread_group_leader(tsk)); return 0; - -killed: - /* protects against exit_notify() and __exit_signal() */ - read_lock(&tasklist_lock); - sig->group_exit_task = NULL; - sig->notify_count = 0; - read_unlock(&tasklist_lock); - return -EAGAIN; }
char *__get_task_comm(char *buf, size_t buf_size, struct task_struct *tsk) @@ -1264,14 +1271,20 @@ int flush_old_exec(struct linux_binprm * bprm) int retval;
/* - * Make sure we have a private signal table and that - * we are unassociated from the previous thread group. + * Make this the only thread in the thread group. */ retval = de_thread(me); if (retval) goto out;
/* + * Make the signal table private. + */ + retval = unshare_sighand(me); + if (retval) + goto out; + + /* * Must be called _before_ exec_mmap() as bprm->mm is * not visibile until then. This also enables the update * to be lockless.