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keys: change keyctl_session_to_parent() to use task_work_add()

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Change keyctl_session_to_parent() to use task_work_add() and move
key_replace_session_keyring() logic into task_work->func().

Note that we do task_work_cancel() before task_work_add() to ensure that
only one work can be pending at any time.  This is important, we must not
allow user-space to abuse the parent's ->task_works list.

The callback, replace_session_keyring(), checks PF_EXITING.  I guess this
is not really needed but looks better.

As a side effect, this fixes the (unlikely) race.  The callers of
key_replace_session_keyring() and keyctl_session_to_parent() lack the
necessary barriers, the parent can miss the request.

Now we can remove task_struct->replacement_session_keyring and related
code.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Howells <dhowells@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexander Gordeev <agordeev@redhat.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David Smith <dsmith@redhat.com>
Cc: "Frank Ch. Eigler" <fche@redhat.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Oleg Nesterov
2012-05-11 10:59:08 +10:00
committed by Al Viro
parent 4d1d61a6b2
commit 413cd3d9ab
4 changed files with 46 additions and 45 deletions
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20
security/keys/process_keys.c
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@@ -834,23 +834,17 @@ error:
* Replace a process's session keyring on behalf of one of its children when
* the target process is about to resume userspace execution.
*/
void key_replace_session_keyring(void)
void key_change_session_keyring(struct task_work *twork)
{
const struct cred *old;
struct cred *new;
const struct cred *old = current_cred();
struct cred *new = twork->data;
if (!current->replacement_session_keyring)
kfree(twork);
if (unlikely(current->flags & PF_EXITING)) {
put_cred(new);
return;
}
write_lock_irq(&tasklist_lock);
new = current->replacement_session_keyring;
current->replacement_session_keyring = NULL;
write_unlock_irq(&tasklist_lock);
if (!new)
return;
old = current_cred();
new-> uid = old-> uid;
new-> euid = old-> euid;
new-> suid = old-> suid;