| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <CAJuCfpFROxDn-Yv48zKw5PuiLd_LQ5+b1Nt4+jEw8wHMWcRDWw@mail.gmail.com>
Date: Wed, 14 Jun 2023 11:19:45 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Tejun Heo <tj@...nel.org>, Lu Jialin <lujialin4@...wei.com>,
Johannes Weiner <hannes@...xchg.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>,
Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2] poll: Fix use-after-free in poll_freewait()
On Wed, Jun 14, 2023 at 10:40 AM Eric Biggers <ebiggers@...nel.org> wrote:
>
> On Wed, Jun 14, 2023 at 03:07:33PM +0800, Lu Jialin wrote:
> > We found a UAF bug in remove_wait_queue as follows:
> >
> > ==================================================================
> > BUG: KASAN: use-after-free in _raw_spin_lock_irqsave+0x71/0xe0
> > Write of size 4 at addr ffff8881150d7b28 by task psi_trigger/15306
> > Call Trace:
> > dump_stack+0x9c/0xd3
> > print_address_description.constprop.0+0x19/0x170
> > __kasan_report.cold+0x6c/0x84
> > kasan_report+0x3a/0x50
> > check_memory_region+0xfd/0x1f0
> > _raw_spin_lock_irqsave+0x71/0xe0
> > remove_wait_queue+0x26/0xc0
> > poll_freewait+0x6b/0x120
> > do_sys_poll+0x305/0x400
> > do_syscall_64+0x33/0x40
> > entry_SYSCALL_64_after_hwframe+0x61/0xc6
> >
> > Allocated by task 15306:
> > kasan_save_stack+0x1b/0x40
> > __kasan_kmalloc.constprop.0+0xb5/0xe0
> > psi_trigger_create.part.0+0xfc/0x450
> > cgroup_pressure_write+0xfc/0x3b0
> > cgroup_file_write+0x1b3/0x390
> > kernfs_fop_write_iter+0x224/0x2e0
> > new_sync_write+0x2ac/0x3a0
> > vfs_write+0x365/0x430
> > ksys_write+0xd5/0x1b0
> > do_syscall_64+0x33/0x40
> > entry_SYSCALL_64_after_hwframe+0x61/0xc6
> >
> > Freed by task 15850:
> > kasan_save_stack+0x1b/0x40
> > kasan_set_track+0x1c/0x30
> > kasan_set_free_info+0x20/0x40
> > __kasan_slab_free+0x151/0x180
> > kfree+0xba/0x680
> > cgroup_file_release+0x5c/0xe0
> > kernfs_drain_open_files+0x122/0x1e0
> > kernfs_drain+0xff/0x1e0
> > __kernfs_remove.part.0+0x1d1/0x3b0
> > kernfs_remove_by_name_ns+0x89/0xf0
> > cgroup_addrm_files+0x393/0x3d0
> > css_clear_dir+0x8f/0x120
> > kill_css+0x41/0xd0
> > cgroup_destroy_locked+0x166/0x300
> > cgroup_rmdir+0x37/0x140
> > kernfs_iop_rmdir+0xbb/0xf0
> > vfs_rmdir.part.0+0xa5/0x230
> > do_rmdir+0x2e0/0x320
> > __x64_sys_unlinkat+0x99/0xc0
> > do_syscall_64+0x33/0x40
> > entry_SYSCALL_64_after_hwframe+0x61/0xc6
> > ==================================================================
> >
> > If using epoll(), wake_up_pollfree will empty waitqueue and set
> > wait_queue_head is NULL before free waitqueue of psi trigger. But is
> > doesn't work when using poll(), which will lead a UAF problem in
> > poll_freewait coms as following:
> >
> > (cgroup_rmdir) |
> > psi_trigger_destroy |
> > wake_up_pollfree(&t->event_wait) |
> > synchronize_rcu(); |
> > kfree(t) |
> > | (poll_freewait)
> > | free_poll_entry(pwq->inline_entries + i)
> > | remove_wait_queue(entry->wait_address)
> > | spin_lock_irqsave(&wq_head->lock)
> >
> > entry->wait_address in poll_freewait() is t->event_wait in cgroup_rmdir().
> > t->event_wait is free in psi_trigger_destroy before call poll_freewait(),
> > therefore wq_head in poll_freewait() has been already freed, which would
> > lead to a UAF.
> >
> > similar problem for epoll() has been fixed commit c2dbe32d5db5
> > ("sched/psi: Fix use-after-free in ep_remove_wait_queue()").
> > epoll wakeup function ep_poll_callback() will empty waitqueue and set
> > wait_queue_head is NULL when pollflags is POLLFREE and judge pwq->whead
> > is NULL or not before remove_wait_queue in ep_remove_wait_queue(),
> > which will fix the UAF bug in ep_remove_wait_queue.
> >
> > But poll wakeup function pollwake() doesn't do that. To fix the
> > problem, we empty waitqueue and set wait_address is NULL in pollwake() when
> > key is POLLFREE. otherwise in remove_wait_queue, which is similar to
> > epoll().
> >
> > Fixes: 0e94682b73bf ("psi: introduce psi monitor")
> > Suggested-by: Suren Baghdasaryan <surenb@...gle.com>
> > Link: https://lore.kernel.org/all/CAJuCfpEoCRHkJF-=1Go9E94wchB4BzwQ1E3vHGWxNe+tEmSJoA@mail.gmail.com/#t
> > Signed-off-by: Lu Jialin <lujialin4@...wei.com>
> > ---
> > v2: correct commit msg and title suggested by Suren Baghdasaryan
> > ---
> > fs/select.c | 20 +++++++++++++++++++-
> > 1 file changed, 19 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/select.c b/fs/select.c
> > index 0ee55af1a55c..e64c7b4e9959 100644
> > --- a/fs/select.c
> > +++ b/fs/select.c
> > @@ -132,7 +132,17 @@ EXPORT_SYMBOL(poll_initwait);
> >
> > static void free_poll_entry(struct poll_table_entry *entry)
> > {
> > - remove_wait_queue(entry->wait_address, &entry->wait);
> > + wait_queue_head_t *whead;
> > +
> > + rcu_read_lock();
> > + /* If it is cleared by POLLFREE, it should be rcu-safe.
> > + * If we read NULL we need a barrier paired with smp_store_release()
> > + * in pollwake().
> > + */
> > + whead = smp_load_acquire(&entry->wait_address);
> > + if (whead)
> > + remove_wait_queue(whead, &entry->wait);
> > + rcu_read_unlock();
> > fput(entry->filp);
> > }
> >
> > @@ -215,6 +225,14 @@ static int pollwake(wait_queue_entry_t *wait, unsigned mode, int sync, void *key
> > entry = container_of(wait, struct poll_table_entry, wait);
> > if (key && !(key_to_poll(key) & entry->key))
> > return 0;
> > + if (key_to_poll(key) & POLLFREE) {
> > + list_del_init(&wait->entry);
> > + /* wait_address !=NULL protects us from the race with
> > + * poll_freewait().
> > + */
> > + smp_store_release(&entry->wait_address, NULL);
> > + return 0;
> > + }
> > return __pollwake(wait, mode, sync, key);
>
> I don't understand why this patch is needed.
>
> The last time I looked at POLLFREE, it is only needed because of asynchronous
> polls. See my explanation in the commit message of commit 50252e4b5e989ce6.
Ah, I missed that. Thanks for the correction.
>
> In summary, POLLFREE solves the problem of polled waitqueues whose lifetime is
> tied to the current task rather than to the file being polled. Also refer to
> the comment above wake_up_pollfree(), which mentions this.
>
> fs/select.c is synchronous polling, not asynchronous. Therefore, it should not
> need to handle POLLFREE.
>
> If there's actually a bug here, most likely it's a bug in psi_trigger_poll()
> where it is using a waitqueue whose lifetime is tied to neither the current task
> nor the file being polled. That needs to be fixed.
Yeah. We discussed this issue in
https://lore.kernel.org/all/CAJuCfpFb0J5ZwO6kncjRG0_4jQLXUy-_dicpH5uGiWP8aKYEJQ@mail.gmail.com
and the root cause is that cgroup_file_release() where
psi_trigger_destroy() is called is not tied to the cgroup file's real
lifetime (see my analysis here:
https://lore.kernel.org/all/CAJuCfpFZ3B4530TgsSHqp5F_gwfrDujwRYewKReJru==MdEHQg@mail.gmail.com/#t).
I guess it's time to do a deeper surgery and figure out a way to call
psi_trigger_destroy() when the polled cgroup file is actually being
destroyed. I'll take a closer look into this later today.
A fix will likely require some cgroup or kernfs code changes, so
CC'ing Tejun for visibility.
Thanks,
Suren.
>
> - Eric
Powered by blists - more mailing lists