Re: [PATCH v6] ceph: fix slab-use-after-free in have_mon_and_osd_map()

[Viacheslav Dubeyko <slava@dubeyko.com>]

Hi Simon,

On Fri, 2025-08-08 at 08:15 +0200, Simon Buttgereit wrote:
> On Wed, 2025-07-02 at 11:12 -0700, Viacheslav Dubeyko wrote:
> > On Tue, 2025-07-01 at 21:57 +0200, Ilya Dryomov wrote:
> > > On Wed, Jun 18, 2025 at 9:16 PM Viacheslav Dubeyko
> > > <slava@dubeyko.com> wrote:
> > > > 
> > > > From: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
> > > > 
> > > > The generic/395 and generic/397 is capable of generating
> > > > the oops is on line net/ceph/ceph_common.c:794 with
> > > > KASAN enabled.
> > > > 
> > > > BUG: KASAN: slab-use-after-free in
> > > > have_mon_and_osd_map+0x56/0x70
> > > > Read of size 4 at addr ffff88811012d810 by task
> > > > mount.ceph/13305
> > > > 
> > > > CPU: 2 UID: 0 PID: 13305 Comm: mount.ceph Not tainted 6.14.0-
> > > > rc2-
> > > > build2+ #1266
> > > > Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014
> > > > Call Trace:
> > > > <TASK>
> > > > dump_stack_lvl+0x57/0x80
> > > > ? have_mon_and_osd_map+0x56/0x70
> > > > print_address_description.constprop.0+0x84/0x330
> > > > ? have_mon_and_osd_map+0x56/0x70
> > > > print_report+0xe2/0x1e0
> > > > ? rcu_read_unlock_sched+0x60/0x80
> > > > ? kmem_cache_debug_flags+0xc/0x20
> > > > ? fixup_red_left+0x17/0x30
> > > > ? have_mon_and_osd_map+0x56/0x70
> > > > kasan_report+0x8d/0xc0
> > > > ? have_mon_and_osd_map+0x56/0x70
> > > > have_mon_and_osd_map+0x56/0x70
> > > > ceph_open_session+0x182/0x290
> > > > ? __pfx_ceph_open_session+0x10/0x10
> > > > ? __init_swait_queue_head+0x8d/0xa0
> > > > ? __pfx_autoremove_wake_function+0x10/0x10
> > > > ? shrinker_register+0xdd/0xf0
> > > > ceph_get_tree+0x333/0x680
> > > > vfs_get_tree+0x49/0x180
> > > > do_new_mount+0x1a3/0x2d0
> > > > ? __pfx_do_new_mount+0x10/0x10
> > > > ? security_capable+0x39/0x70
> > > > path_mount+0x6dd/0x730
> > > > ? __pfx_path_mount+0x10/0x10
> > > > ? kmem_cache_free+0x1e5/0x270
> > > > ? user_path_at+0x48/0x60
> > > > do_mount+0x99/0xe0
> > > > ? __pfx_do_mount+0x10/0x10
> > > > ? lock_release+0x155/0x190
> > > > __do_sys_mount+0x141/0x180
> > > > do_syscall_64+0x9f/0x100
> > > > entry_SYSCALL_64_after_hwframe+0x76/0x7e
> > > > RIP: 0033:0x7f01b1b14f3e
> > > > Code: 48 8b 0d d5 3e 0f 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e
> > > > 0f
> > > > 1f 84 00 00 00 00 00 90 f3 0f 1e fa 49 89 ca b8 a5 00 00 00 0f
> > > > 05
> > > > <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d a2 3e 0f 00 f7 d8 64 89
> > > > 01
> > > > 48
> > > > RSP: 002b:00007fffd129fa08 EFLAGS: 00000246 ORIG_RAX:
> > > > 00000000000000a5
> > > > RAX: ffffffffffffffda RBX: 0000564ec01a7850 RCX:
> > > > 00007f01b1b14f3e
> > > > RDX: 0000564ec00f2225 RSI: 00007fffd12a1964 RDI:
> > > > 0000564ec0147a20
> > > > RBP: 00007fffd129fbd0 R08: 0000564ec014da90 R09:
> > > > 0000000000000080
> > > > R10: 0000000000000000 R11: 0000000000000246 R12:
> > > > 00007fffd12a194e
> > > > R13: 0000000000000000 R14: 00007fffd129fa50 R15:
> > > > 00007fffd129fa40
> > > > </TASK>
> > > > 
> > > > Allocated by task 13305:
> > > > stack_trace_save+0x8c/0xc0
> > > > kasan_save_stack+0x1e/0x40
> > > > kasan_save_track+0x10/0x30
> > > > __kasan_kmalloc+0x3a/0x50
> > > > __kmalloc_noprof+0x247/0x290
> > > > ceph_osdmap_alloc+0x16/0x130
> > > > ceph_osdc_init+0x27a/0x4c0
> > > > ceph_create_client+0x153/0x190
> > > > create_fs_client+0x50/0x2a0
> > > > ceph_get_tree+0xff/0x680
> > > > vfs_get_tree+0x49/0x180
> > > > do_new_mount+0x1a3/0x2d0
> > > > path_mount+0x6dd/0x730
> > > > do_mount+0x99/0xe0
> > > > __do_sys_mount+0x141/0x180
> > > > do_syscall_64+0x9f/0x100
> > > > entry_SYSCALL_64_after_hwframe+0x76/0x7e
> > > > 
> > > > Freed by task 9475:
> > > > stack_trace_save+0x8c/0xc0
> > > > kasan_save_stack+0x1e/0x40
> > > > kasan_save_track+0x10/0x30
> > > > kasan_save_free_info+0x3b/0x50
> > > > __kasan_slab_free+0x18/0x30
> > > > kfree+0x212/0x290
> > > > handle_one_map+0x23c/0x3b0
> > > > ceph_osdc_handle_map+0x3c9/0x590
> > > > mon_dispatch+0x655/0x6f0
> > > > ceph_con_process_message+0xc3/0xe0
> > > > ceph_con_v1_try_read+0x614/0x760
> > > > ceph_con_workfn+0x2de/0x650
> > > > process_one_work+0x486/0x7c0
> > > > process_scheduled_works+0x73/0x90
> > > > worker_thread+0x1c8/0x2a0
> > > > kthread+0x2ec/0x300
> > > > ret_from_fork+0x24/0x40
> > > > ret_from_fork_asm+0x1a/0x30
> > > > 
> > > > The buggy address belongs to the object at ffff88811012d800
> > > > which belongs to the cache kmalloc-512 of size 512
> > > > The buggy address is located 16 bytes inside of
> > > > freed 512-byte region [ffff88811012d800, ffff88811012da00)
> > > > 
> > > > The buggy address belongs to the physical page:
> > > > page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0
> > > > pfn:0x11012c
> > > > head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0
> > > > pincount:0
> > > > flags: 0x200000000000040(head|node=0|zone=2)
> > > > page_type: f5(slab)
> > > > raw: 0200000000000040 ffff888100042c80 dead000000000100
> > > > dead000000000122
> > > > raw: 0000000000000000 0000000080100010 00000000f5000000
> > > > 0000000000000000
> > > > head: 0200000000000040 ffff888100042c80 dead000000000100
> > > > dead000000000122
> > > > head: 0000000000000000 0000000080100010 00000000f5000000
> > > > 0000000000000000
> > > > head: 0200000000000002 ffffea0004404b01 ffffffffffffffff
> > > > 0000000000000000
> > > > head: 0000000000000004 0000000000000000 00000000ffffffff
> > > > 0000000000000000
> > > > page dumped because: kasan: bad access detected
> > > > 
> > > > Memory state around the buggy address:
> > > > ffff88811012d700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > > > fc
> > > > ffff88811012d780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > > > fc
> > > > 
> > > >     ffff88811012d800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb
> > > > fb
> > > > fb
> > > > 
> > > > ^
> > > > ffff88811012d880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > > > fb
> > > > ffff88811012d900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > > > fb
> > > > ===============================================================
> > > > ==
> > > > =
> > > > Disabling lock debugging due to kernel taint
> > > > libceph: client274326 fsid 8598140e-35c2-11ee-b97c-001517c545cc
> > > > libceph: mon0 (1)90.155.74.19:6789 session established
> > > > libceph: client274327 fsid 8598140e-35c2-11ee-b97c-001517c545cc
> > > > 
> > > > We have such scenario:
> > > > 
> > > > Thread 1:
> > > > void ceph_osdmap_destroy(...) {
> > > >     <skipped>
> > > >     kfree(map);
> > > > }
> > > > Thread 1 sleep...
> > > > 
> > > > Thread 2:
> > > > static bool have_mon_and_osd_map(struct ceph_client *client) {
> > > >     return client->monc.monmap && client->monc.monmap->epoch &&
> > > >         client->osdc.osdmap && client->osdc.osdmap->epoch;
> > > > }
> > > > Thread 2 has oops...
> > > > 
> > > > Thread 1 wake up:
> > > > static int handle_one_map(...) {
> > > >     <skipped>
> > > >     osdc->osdmap = newmap;
> > > >     <skipped>
> > > > }
> > > > 
> > > > This patch fixes the issue by means of locking
> > > > client->osdc.lock and client->monc.mutex before
> > > > the checking client->osdc.osdmap and
> > > > client->monc.monmap in have_mon_and_osd_map() function.
> > > > Patch adds locking in the ceph_osdc_stop()
> > > > method during the destructruction of osdc->osdmap and
> > > > assigning of NULL to the pointer. The lock is used
> > > > in the ceph_monc_stop() during the freeing of monc->monmap
> > > > and assigning NULL to the pointer too. The monmap_show()
> > > > and osdmap_show() methods were reworked to prevent
> > > > the potential race condition during the methods call.
> > > > 
> > > > Reported-by: David Howells <dhowells@redhat.com>
> > > > Signed-off-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
> > > > ---
> > > >  net/ceph/ceph_common.c | 34 +++++++++++++++++++++++++++++-----
> > > >  net/ceph/debugfs.c     | 17 +++++++++++++----
> > > >  net/ceph/mon_client.c  |  9 ++++++++-
> > > >  net/ceph/osd_client.c  |  4 ++++
> > > >  4 files changed, 54 insertions(+), 10 deletions(-)
> > > > 
> > > > diff --git a/net/ceph/ceph_common.c b/net/ceph/ceph_common.c
> > > > index 4c6441536d55..a28b29c763ca 100644
> > > > --- a/net/ceph/ceph_common.c
> > > > +++ b/net/ceph/ceph_common.c
> > > > @@ -790,8 +790,18 @@ EXPORT_SYMBOL(ceph_reset_client_addr);
> > > >   */
> > > >  static bool have_mon_and_osd_map(struct ceph_client *client)
> > > >  {
> > > > -       return client->monc.monmap && client->monc.monmap-
> > > > >epoch
> > > > &&
> > > > -              client->osdc.osdmap && client->osdc.osdmap-
> > > > >epoch;
> > > > +       bool have_mon_map = false;
> > > > +       bool have_osd_map = false;
> > > > +
> > > > +       mutex_lock(&client->monc.mutex);
> > > > +       have_mon_map = client->monc.monmap && client-
> > > > > monc.monmap-
> > > > > epoch;
> > > > +       mutex_unlock(&client->monc.mutex);
> > > > +
> > > > +       down_read(&client->osdc.lock);
> > > > +       have_osd_map = client->osdc.osdmap && client-
> > > > > osdc.osdmap-
> > > > > epoch;
> > > > +       up_read(&client->osdc.lock);
> > > > +
> > > > +       return have_mon_map && have_osd_map;
> > > >  }
> > > > 
> > > >  /*
> > > > @@ -813,9 +823,23 @@ int __ceph_open_session(struct ceph_client
> > > > *client, unsigned long started)
> > > > 
> > > >                 /* wait */
> > > >                 dout("mount waiting for mon_map\n");
> > > > -               err = wait_event_interruptible_timeout(client-
> > > > > auth_wq,
> > > > -                       have_mon_and_osd_map(client) ||
> > > > (client-
> > > > > auth_err < 0),
> > > > -                       ceph_timeout_jiffies(timeout));
> > > > +
> > > > +               DEFINE_WAIT_FUNC(wait, woken_wake_function);
> > > > +
> > > > +               add_wait_queue(&client->auth_wq, &wait);
> > > > +
> > > > +               while (!(have_mon_and_osd_map(client) ||
> > > > +                                       (client->auth_err <
> > > > 0)))
> > > > {
> > > 
> > > Hi Slava,
> > > 
> > > This looks much better but misses two points raised in the
> > > comments
> > > on
> > > previous versions.  The first point is that it would be better to
> > > access client->auth_err under client->monc.mutex, matching how
> > > it's
> > > set
> > > in finish_auth() -- now that locks can be freely taken here it
> > > should
> > > be a trivial change.
> > > 
> > 
> > OK. Let me rework the patch. I hope it will be trivial change. :)
> > 
> > > > +                       if (signal_pending(current)) {
> > > > +                               err = -ERESTARTSYS;
> > > > +                               break;
> > > > +                       }
> > > > +                       wait_woken(&wait, TASK_INTERRUPTIBLE,
> > > > +                                 
> > > > ceph_timeout_jiffies(timeout));
> > > > +               }
> > > > +
> > > > +               remove_wait_queue(&client->auth_wq, &wait);
> > > > +
> > > >                 if (err < 0)
> > > >                         return err;
> > > >                 if (client->auth_err < 0)
> > > 
> > > Separately, I wonder if the new nested loop which checks both for
> > > the
> > > presence of maps and client->auth_err could be merged into the
> > > existing
> > > outer loop which currently checks for the presence of maps in the
> > > loop
> > > condition and client->auth_err here in the loop body.  Having a
> > > single
> > > loop with everything checked in just one place would be a lot
> > > cleaner.
> > > 
> > 
> > Let me take a deeper look into the code. I hope I follow your
> > point.
> > 
> > > > diff --git a/net/ceph/debugfs.c b/net/ceph/debugfs.c
> > > > index 2110439f8a24..7b45c169a859 100644
> > > > --- a/net/ceph/debugfs.c
> > > > +++ b/net/ceph/debugfs.c
> > > > @@ -36,8 +36,10 @@ static int monmap_show(struct seq_file *s,
> > > > void
> > > > *p)
> > > >         int i;
> > > >         struct ceph_client *client = s->private;
> > > > 
> > > > +       mutex_lock(&client->monc.mutex);
> > > > +
> > > >         if (client->monc.monmap == NULL)
> > > > -               return 0;
> > > > +               goto out_unlock;
> > > > 
> > > >         seq_printf(s, "epoch %d\n", client->monc.monmap-
> > > > >epoch);
> > > >         for (i = 0; i < client->monc.monmap->num_mon; i++) {
> > > > @@ -48,6 +50,10 @@ static int monmap_show(struct seq_file *s,
> > > > void
> > > > *p)
> > > >                            ENTITY_NAME(inst->name),
> > > >                            ceph_pr_addr(&inst->addr));
> > > >         }
> > > > +
> > > > +out_unlock:
> > > > +       mutex_unlock(&client->monc.mutex);
> > > > +
> > > >         return 0;
> > > >  }
> > > > 
> > > > @@ -56,13 +62,15 @@ static int osdmap_show(struct seq_file *s,
> > > > void
> > > > *p)
> > > >         int i;
> > > >         struct ceph_client *client = s->private;
> > > >         struct ceph_osd_client *osdc = &client->osdc;
> > > > -       struct ceph_osdmap *map = osdc->osdmap;
> > > > +       struct ceph_osdmap *map = NULL;
> > > >         struct rb_node *n;
> > > > 
> > > > +       down_read(&osdc->lock);
> > > > +
> > > > +       map = osdc->osdmap;
> > > >         if (map == NULL)
> > > > -               return 0;
> > > > +               goto out_unlock;
> > > > 
> > > > -       down_read(&osdc->lock);
> > > >         seq_printf(s, "epoch %u barrier %u flags 0x%x\n", map-
> > > > > epoch,
> > > >                         osdc->epoch_barrier, map->flags);
> > > > 
> > > > @@ -131,6 +139,7 @@ static int osdmap_show(struct seq_file *s,
> > > > void
> > > > *p)
> > > >                 seq_printf(s, "]\n");
> > > >         }
> > > > 
> > > > +out_unlock:
> > > >         up_read(&osdc->lock);
> > > >         return 0;
> > > >  }
> > > > diff --git a/net/ceph/mon_client.c b/net/ceph/mon_client.c
> > > > index ab66b599ac47..b299e5bbddb1 100644
> > > > --- a/net/ceph/mon_client.c
> > > > +++ b/net/ceph/mon_client.c
> > > > @@ -1232,6 +1232,7 @@ int ceph_monc_init(struct ceph_mon_client
> > > > *monc, struct ceph_client *cl)
> > > >         ceph_auth_destroy(monc->auth);
> > > >  out_monmap:
> > > >         kfree(monc->monmap);
> > > > +       monc->monmap = NULL;
> > > >  out:
> > > >         return err;
> > > >  }
> > > > @@ -1239,6 +1240,8 @@ EXPORT_SYMBOL(ceph_monc_init);
> > > > 
> > > >  void ceph_monc_stop(struct ceph_mon_client *monc)
> > > >  {
> > > > +       struct ceph_monmap *old_monmap;
> > > > +
> > > >         dout("stop\n");
> > > > 
> > > >         mutex_lock(&monc->mutex);
> > > > @@ -1266,7 +1269,11 @@ void ceph_monc_stop(struct
> > > > ceph_mon_client
> > > > *monc)
> > > >         ceph_msg_put(monc->m_subscribe);
> > > >         ceph_msg_put(monc->m_subscribe_ack);
> > > > 
> > > > -       kfree(monc->monmap);
> > > > +       mutex_lock(&monc->mutex);
> > > > +       old_monmap = monc->monmap;
> > > > +       monc->monmap = NULL;
> > > > +       mutex_unlock(&monc->mutex);
> > > > +       kfree(old_monmap);
> > > 
> > > The second point is that locking (or any changes at all) in
> > > ceph_monc_stop() and ceph_osdc_stop() shouldn't be needed.  As
> > > mentioned before, it's the point of no return where the entire
> > > client
> > > including monc and osdc parts gets freed very shortly after.
> > > 
> > 
> > I see. You still dislike this locking logic here. :) OK. I can
> > rework
> > it too.
> > 
> > Thanks,
> > Slava.
> 
> Hi Slava,
> first thanks for your work. We stumbled over the same use-after-free
> some weeks 
> ago and I was grateful, that somebody else already found it and a
> patch
> is discussed. 
> 
> I have a query regarding the status of your patch: 
> Do you have any updates on its progress, or can you estimate when it
> might be integrated into the upstream sources?

I already have shared v7 of this patch [1]. :) I hope Ilya will be
happy this time. :) I am going to apply this patch on testing branch
today. So, probably, we could send the patch to upstream during next
merge window.

Thanks,
Slava. 

[1]
https://lore.kernel.org/ceph-devel/20250703174128.500301-1-slava@dubeyko.com/T/#u