From 43e13cc107cf6cd3c15fbe1cef849435c2223d50 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 31 May 2012 16:26:16 -0700 Subject: [PATCH] cred: remove task_is_dead() from __task_cred() validation Commit 8f92054e7ca1 ("CRED: Fix __task_cred()'s lockdep check and banner comment"): add the following validation condition: task->exit_state >= 0 to permit the access if the target task is dead and therefore unable to change its own credentials. OK, but afaics currently this can only help wait_task_zombie() which calls __task_cred() without rcu lock. Remove this validation and change wait_task_zombie() to use task_uid() instead. This means we do rcu_read_lock() only to shut up the lockdep, but we already do the same in, say, wait_task_stopped(). task_is_dead() should die, task->exit_state != 0 means that this task has passed exit_notify(), only do_wait-like code paths should use this. Unfortunately, we can't kill task_is_dead() right now, it has already acquired buggy users in drivers/staging. The fix already exists. Signed-off-by: Oleg Nesterov Reviewed-by: "Eric W. Biederman" Acked-by: David Howells Cc: Jiri Olsa Cc: Paul E. McKenney Cc: James Morris Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/cred.h | 10 +++------- kernel/exit.c | 2 +- 2 files changed, 4 insertions(+), 8 deletions(-) diff --git a/include/linux/cred.h b/include/linux/cred.h index 917dc5aeb1d4..ebbed2ce6637 100644 --- a/include/linux/cred.h +++ b/include/linux/cred.h @@ -277,17 +277,13 @@ static inline void put_cred(const struct cred *_cred) * @task: The task to query * * Access the objective credentials of a task. The caller must hold the RCU - * readlock or the task must be dead and unable to change its own credentials. + * readlock. * * The result of this function should not be passed directly to get_cred(); * rather get_task_cred() should be used instead. */ -#define __task_cred(task) \ - ({ \ - const struct task_struct *__t = (task); \ - rcu_dereference_check(__t->real_cred, \ - task_is_dead(__t)); \ - }) +#define __task_cred(task) \ + rcu_dereference((task)->real_cred) /** * get_current_cred - Get the current task's subjective credentials diff --git a/kernel/exit.c b/kernel/exit.c index 910a0716e17a..3281493ce7ad 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -1214,7 +1214,7 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p) unsigned long state; int retval, status, traced; pid_t pid = task_pid_vnr(p); - uid_t uid = from_kuid_munged(current_user_ns(), __task_cred(p)->uid); + uid_t uid = from_kuid_munged(current_user_ns(), task_uid(p)); struct siginfo __user *infop; if (!likely(wo->wo_flags & WEXITED))