libceph: fix potential use-after-free in have_mon_and_osd_map()

The wait loop in __ceph_open_session() can race with the client
receiving a new monmap or osdmap shortly after the initial map is
received. Both ceph_monc_handle_map() and handle_one_map() install
a new map immediately after freeing the old one

kfree(monc->monmap);
monc->monmap = monmap;

ceph_osdmap_destroy(osdc->osdmap);
osdc->osdmap = newmap;

under client->monc.mutex and client->osdc.lock respectively, but
because neither is taken in have_mon_and_osd_map() it's possible for
client->monc.monmap->epoch and client->osdc.osdmap->epoch arms in

client->monc.monmap && client->monc.monmap->epoch &&
client->osdc.osdmap && client->osdc.osdmap->epoch;

condition to dereference an already freed map. This happens to be
reproducible with generic/395 and generic/397 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
...
Call Trace:
<TASK>
have_mon_and_osd_map+0x56/0x70
ceph_open_session+0x182/0x290
ceph_get_tree+0x333/0x680
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
</TASK>

Allocated by task 13305:
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:
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

Rewrite the wait loop to check the above condition directly with
client->monc.mutex and client->osdc.lock taken as appropriate. While
at it, improve the timeout handling (previously mount_timeout could be
exceeded in case wait_event_interruptible_timeout() slept more than
once) and access client->auth_err under client->monc.mutex to match
how it's set in finish_auth().

monmap_show() and osdmap_show() now take the respective lock before
accessing the map as well.

Cc: [e-mail]
Reported-by: David Howells <[e-mail]>
Signed-off-by: Ilya Dryomov <[e-mail]>
Reviewed-by: Viacheslav Dubeyko <[e-mail]>

net/ceph/ceph_common.c

···
 EXPORT_SYMBOL(ceph_reset_client_addr);
 
 /*
- * true if we have the mon map (and have thus joined the cluster)
- */
-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;
-}
-
-/*
  * mount: join the ceph cluster, and open root directory.
  */
 int __ceph_open_session(struct ceph_client *client, unsigned long started)
 {
-	unsigned long timeout = client->options->mount_timeout;
-	long err;
+	DEFINE_WAIT_FUNC(wait, woken_wake_function);
+	long timeout = ceph_timeout_jiffies(client->options->mount_timeout);
+	bool have_monmap, have_osdmap;
+	int err;
 
 	/* open session, and wait for mon and osd maps */
 	err = ceph_monc_open_session(&client->monc);
 	if (err < 0)
 		return err;
 
-	while (!have_mon_and_osd_map(client)) {
-		if (timeout && time_after_eq(jiffies, started + timeout))
-			return -ETIMEDOUT;
+	add_wait_queue(&client->auth_wq, &wait);
+	for (;;) {
+		mutex_lock(&client->monc.mutex);
+		err = client->auth_err;
+		have_monmap = client->monc.monmap && client->monc.monmap->epoch;
+		mutex_unlock(&client->monc.mutex);
+
+		down_read(&client->osdc.lock);
+		have_osdmap = client->osdc.osdmap && client->osdc.osdmap->epoch;
+		up_read(&client->osdc.lock);
+
+		if (err || (have_monmap && have_osdmap))
+			break;
+
+		if (signal_pending(current)) {
+			err = -ERESTARTSYS;
+			break;
+		}
+
+		if (!timeout) {
+			err = -ETIMEDOUT;
+			break;
+		}
 
 		/* 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));
-		if (err < 0)
-			return err;
-		if (client->auth_err < 0)
-			return client->auth_err;
+		timeout = wait_woken(&wait, TASK_INTERRUPTIBLE, timeout);
 	}
+	remove_wait_queue(&client->auth_wq, &wait);
+
+	if (err)
+		return err;
 
 	pr_info("client%llu fsid %pU\n", ceph_client_gid(client),
 		&client->fsid);

net/ceph/debugfs.c

···
 	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++) {
···
 			   ENTITY_NAME(inst->name),
 			   ceph_pr_addr(&inst->addr));
 	}
+
+out_unlock:
+	mutex_unlock(&client->monc.mutex);
 	return 0;
 }
 
···
 	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;
 	struct rb_node *n;
 
-	if (map == NULL)
-		return 0;
-
 	down_read(&osdc->lock);
+	map = osdc->osdmap;
+	if (map == NULL)
+		goto out_unlock;
+
 	seq_printf(s, "epoch %u barrier %u flags 0x%x\n", map->epoch,
 			osdc->epoch_barrier, map->flags);
 
···
 		seq_printf(s, "]\n");
 	}
 
+out_unlock:
 	up_read(&osdc->lock);
 	return 0;
 }