Messages in this thread Patch in this message | | | Date | Tue, 10 Apr 2012 21:46:25 +0200 | From | Oleg Nesterov <> | Subject | [PATCH 1/1] creds: kill __task_cred()->task_is_dead() validation |
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commit 8f92054e:
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 found the bugy users in drivers/staging/, the fix already exists.
Signed-off-by: Oleg Nesterov <oleg@redhat.com> --- 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 adadf71..1b64c72 100644 --- a/include/linux/cred.h +++ b/include/linux/cred.h @@ -276,17 +276,13 @@ 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 4b4042f..7b36288 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -1214,7 +1213,7 @@ 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 = __task_cred(p)->uid; + uid_t uid = task_uid(p); struct siginfo __user *infop; if (!likely(wo->wo_flags & WEXITED)) -- 1.5.5.1
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