Re: [PATCH] CRED: Fix regression in cap_capable() as shown up by sys_faccessat() [ver #2]

David Howells
2009-01-05T13:11:40Z

J. Bruce Fields <bfields@fieldses.org> wrote:

> > > > No. I started bisecting, and it does appear to be a regression from the
> > > > cred patches, but at some point in the middle there it hangs on boot (a
> > > > softlockup report blames a spinlock in set_groups).
> > >
> > > Do you remember which patch you were at?
>
> More precisely:
> - The last working commit is b6dff3ec... "CRED: Separate task
> security context from task_struct".
> - The first commit exhibiting the permissions problem is
> a6f76f2... "CRED: Make execve() take advantage of
> copy-on-write credentials".

I presume by 'first' you mean 'latest'.

> - The 9 commits in between (from f1752eec to d84f4f9) result in
> a soft lookup on boot.

I think the problem may be that f1752eec removes the lock initialisation for
init_cred from the INIT_CRED() macro:

- .lock = __SPIN_LOCK_UNLOCKED(p.lock), \

but doesn't add it to the out of line init_cred:

+struct cred init_cred = {
+ .usage = ATOMIC_INIT(3),
+ .securebits = SECUREBITS_DEFAULT,
+ .cap_inheritable = CAP_INIT_INH_SET,
+ .cap_permitted = CAP_FULL_SET,
+ .cap_effective = CAP_INIT_EFF_SET,
+ .cap_bset = CAP_INIT_BSET,
+ .user = INIT_USER,
+ .group_info = &init_groups,
+};

Can you try adding:

.lock = __SPIN_LOCK_UNLOCKED(init_cred.lock),

to that and also add:

spin_lock_init(&pcred->lock);

into copy_creds() see if the problem goes away?

I'm a bit surprised that lockdep doesn't bark at this one - I thought it
checked for lock initialisation.

David