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Commit 43e13cc1 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

cred: remove task_is_dead() from __task_cred() validation 



Commit 8f92054e ("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: default avatarOleg Nesterov <oleg@redhat.com>
Reviewed-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: default avatarDavid Howells <dhowells@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 9b3c98cd

include/linux/cred.h

+3 −7
Original line number Diff line number Diff line
@@ -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));		\

	})

	rcu_dereference((task)->real_cred)



/**

 * get_current_cred - Get the current task's subjective credentials

kernel/exit.c

+1 −1
Original line number Diff line number Diff line
@@ -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))