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CRED: Use RCU to access another task's creds and to release a task's own creds

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Use RCU to access another task's creds and to release a task's own creds.
This means that it will be possible for the credentials of a task to be
replaced without another task (a) requiring a full lock to read them, and (b)
seeing deallocated memory.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
This commit is contained in:
David Howells
2008-11-14 10:39:19 +11:00
committed by James Morris
parent 86a264abe5
commit c69e8d9c01
28 changed files with 353 additions and 202 deletions
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14
kernel/exit.c
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@ -160,7 +160,10 @@ void release_task(struct task_struct * p)
int zap_leader;
repeat:
tracehook_prepare_release_task(p);
atomic_dec(&p->cred->user->processes);
/* don't need to get the RCU readlock here - the process is dead and
* can't be modifying its own credentials */
atomic_dec(&__task_cred(p)->user->processes);
proc_flush_task(p);
write_lock_irq(&tasklist_lock);
tracehook_finish_release_task(p);
@ -1267,12 +1270,12 @@ static int wait_task_zombie(struct task_struct *p, int options,
unsigned long state;
int retval, status, traced;
pid_t pid = task_pid_vnr(p);
uid_t uid = __task_cred(p)->uid;
if (!likely(options & WEXITED))
return 0;
if (unlikely(options & WNOWAIT)) {
uid_t uid = p->cred->uid;
int exit_code = p->exit_code;
int why, status;
@ -1393,7 +1396,7 @@ static int wait_task_zombie(struct task_struct *p, int options,
if (!retval && infop)
retval = put_user(pid, &infop->si_pid);
if (!retval && infop)
retval = put_user(p->cred->uid, &infop->si_uid);
retval = put_user(uid, &infop->si_uid);
if (!retval)
retval = pid;
@ -1458,7 +1461,8 @@ static int wait_task_stopped(int ptrace, struct task_struct *p,
if (!unlikely(options & WNOWAIT))
p->exit_code = 0;
uid = p->cred->uid;
/* don't need the RCU readlock here as we're holding a spinlock */
uid = __task_cred(p)->uid;
unlock_sig:
spin_unlock_irq(&p->sighand->siglock);
if (!exit_code)
@ -1532,10 +1536,10 @@ static int wait_task_continued(struct task_struct *p, int options,
}
if (!unlikely(options & WNOWAIT))
p->signal->flags &= ~SIGNAL_STOP_CONTINUED;
uid = __task_cred(p)->uid;
spin_unlock_irq(&p->sighand->siglock);
pid = task_pid_vnr(p);
uid = p->cred->uid;
get_task_struct(p);
read_unlock(&tasklist_lock);