RDMA/ucma: Fix use-after-free bug in ucma_create_uevent

ucma_process_join() allocates struct ucma_multicast mc and frees it if an
error occurs during its run.  Specifically, if an error occurs in
copy_to_user(), a use-after-free might happen in the following scenario:

1. mc struct is allocated.
2. rdma_join_multicast() is called and succeeds. During its run,
   cma_iboe_join_multicast() enqueues a work that will later use the
   aforementioned mc struct.
3. copy_to_user() is called and fails.
4. mc struct is deallocated.
5. The work that was enqueued by cma_iboe_join_multicast() is run and
   calls ucma_create_uevent() which tries to access mc struct (which is
   freed by now).

Fix this bug by cancelling the work enqueued by cma_iboe_join_multicast().
Since cma_work_handler() frees struct cma_work, we don't use it in
cma_iboe_join_multicast() so we can safely cancel the work later.

The following syzkaller report revealed it:

   BUG: KASAN: use-after-free in ucma_create_uevent+0x2dd/0x;3f0 drivers/infiniband/core/ucma.c:272
   Read of size 8 at addr ffff88810b3ad110 by task kworker/u8:1/108

   CPU: 1 PID: 108 Comm: kworker/u8:1 Not tainted 5.10.0-rc6+ #257
   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS   rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
   Workqueue: rdma_cm cma_work_handler
   Call Trace:
    __dump_stack lib/dump_stack.c:77 [inline]
    dump_stack+0xbe/0xf9 lib/dump_stack.c:118
    print_address_description.constprop.0+0x3e/0×60 mm/kasan/report.c:385
    __kasan_report mm/kasan/report.c:545 [inline]
    kasan_report.cold+0x1f/0×37 mm/kasan/report.c:562
    ucma_create_uevent+0x2dd/0×3f0 drivers/infiniband/core/ucma.c:272
    ucma_event_handler+0xb7/0×3c0 drivers/infiniband/core/ucma.c:349
    cma_cm_event_handler+0x5d/0×1c0 drivers/infiniband/core/cma.c:1977
    cma_work_handler+0xfa/0×190 drivers/infiniband/core/cma.c:2718
    process_one_work+0x54c/0×930 kernel/workqueue.c:2272
    worker_thread+0x82/0×830 kernel/workqueue.c:2418
    kthread+0x1ca/0×220 kernel/kthread.c:292
    ret_from_fork+0x1f/0×30 arch/x86/entry/entry_64.S:296

   Allocated by task 359:
     kasan_save_stack+0x1b/0×40 mm/kasan/common.c:48
     kasan_set_track mm/kasan/common.c:56 [inline]
     __kasan_kmalloc mm/kasan/common.c:461 [inline]
     __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:434
     kmalloc include/linux/slab.h:552 [inline]
     kzalloc include/linux/slab.h:664 [inline]
     ucma_process_join+0x16e/0×3f0 drivers/infiniband/core/ucma.c:1453
     ucma_join_multicast+0xda/0×140 drivers/infiniband/core/ucma.c:1538
     ucma_write+0x1f7/0×280 drivers/infiniband/core/ucma.c:1724
     vfs_write fs/read_write.c:603 [inline]
     vfs_write+0x191/0×4c0 fs/read_write.c:585
     ksys_write+0x1a1/0×1e0 fs/read_write.c:658
     do_syscall_64+0x2d/0×40 arch/x86/entry/common.c:46
     entry_SYSCALL_64_after_hwframe+0x44/0xa9

   Freed by task 359:
     kasan_save_stack+0x1b/0×40 mm/kasan/common.c:48
     kasan_set_track+0x1c/0×30 mm/kasan/common.c:56
     kasan_set_free_info+0x1b/0×30 mm/kasan/generic.c:355
     __kasan_slab_free+0x112/0×160 mm/kasan/common.c:422
     slab_free_hook mm/slub.c:1544 [inline]
     slab_free_freelist_hook mm/slub.c:1577 [inline]
     slab_free mm/slub.c:3142 [inline]
     kfree+0xb3/0×3e0 mm/slub.c:4124
     ucma_process_join+0x22d/0×3f0 drivers/infiniband/core/ucma.c:1497
     ucma_join_multicast+0xda/0×140 drivers/infiniband/core/ucma.c:1538
     ucma_write+0x1f7/0×280 drivers/infiniband/core/ucma.c:1724
     vfs_write fs/read_write.c:603 [inline]
     vfs_write+0x191/0×4c0 fs/read_write.c:585
     ksys_write+0x1a1/0×1e0 fs/read_write.c:658
     do_syscall_64+0x2d/0×40 arch/x86/entry/common.c:46
     entry_SYSCALL_64_after_hwframe+0x44/0xa9
     The buggy address belongs to the object at ffff88810b3ad100
     which belongs to the cache kmalloc-192 of size 192
     The buggy address is located 16 bytes inside of
     192-byte region [ffff88810b3ad100, ffff88810b3ad1c0)

Fixes: b5de0c60 ("RDMA/cma: Fix use after free race in roce multicast join")
Link: https://lore.kernel.org/r/20210211090517.1278415-1-leon@kernel.orgReported-by: NAmit Matityahu <mitm@nvidia.com>
Signed-off-by: NAvihai Horon <avihaih@nvidia.com>
Signed-off-by: NLeon Romanovsky <leonro@nvidia.com>
Signed-off-by: NJason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/core/cma.c

@@ -352,7 +352,13 @@ struct ib_device *cma_get_ib_dev(struct cma_device *cma_dev)
 
 struct cma_multicast {
 	struct rdma_id_private *id_priv;
-	struct ib_sa_multicast *sa_mc;
+	union {
+		struct ib_sa_multicast *sa_mc;
+		struct {
+			struct work_struct work;
+			struct rdma_cm_event event;
+		} iboe_join;
+	};
 	struct list_head	list;
 	void			*context;
 	struct sockaddr_storage	addr;
@@ -1823,6 +1829,8 @@ static void destroy_mc(struct rdma_id_private *id_priv,
 			cma_igmp_send(ndev, &mgid, false);
 			dev_put(ndev);
 		}
+
+		cancel_work_sync(&mc->iboe_join.work);
 	}
 	kfree(mc);
 }
@@ -2683,6 +2691,28 @@ static int cma_query_ib_route(struct rdma_id_private *id_priv,
 	return (id_priv->query_id < 0) ? id_priv->query_id : 0;
 }
 
+static void cma_iboe_join_work_handler(struct work_struct *work)
+{
+	struct cma_multicast *mc =
+		container_of(work, struct cma_multicast, iboe_join.work);
+	struct rdma_cm_event *event = &mc->iboe_join.event;
+	struct rdma_id_private *id_priv = mc->id_priv;
+	int ret;
+
+	mutex_lock(&id_priv->handler_mutex);
+	if (READ_ONCE(id_priv->state) == RDMA_CM_DESTROYING ||
+	    READ_ONCE(id_priv->state) == RDMA_CM_DEVICE_REMOVAL)
+		goto out_unlock;
+
+	ret = cma_cm_event_handler(id_priv, event);
+	WARN_ON(ret);
+
+out_unlock:
+	mutex_unlock(&id_priv->handler_mutex);
+	if (event->event == RDMA_CM_EVENT_MULTICAST_JOIN)
+		rdma_destroy_ah_attr(&event->param.ud.ah_attr);
+}
+
 static void cma_work_handler(struct work_struct *_work)
 {
 	struct cma_work *work = container_of(_work, struct cma_work, work);
@@ -4478,10 +4508,7 @@ static int cma_ib_mc_handler(int status, struct ib_sa_multicast *multicast)
 	cma_make_mc_event(status, id_priv, multicast, &event, mc);
 	ret = cma_cm_event_handler(id_priv, &event);
 	rdma_destroy_ah_attr(&event.param.ud.ah_attr);
-	if (ret) {
-		destroy_id_handler_unlock(id_priv);
-		return 0;
-	}
+	WARN_ON(ret);
 
 out:
 	mutex_unlock(&id_priv->handler_mutex);
@@ -4593,7 +4620,6 @@ static void cma_iboe_set_mgid(struct sockaddr *addr, union ib_gid *mgid,
 static int cma_iboe_join_multicast(struct rdma_id_private *id_priv,
 				   struct cma_multicast *mc)
 {
-	struct cma_work *work;
 	struct rdma_dev_addr *dev_addr = &id_priv->id.route.addr.dev_addr;
 	int err = 0;
 	struct sockaddr *addr = (struct sockaddr *)&mc->addr;
@@ -4607,10 +4633,6 @@ static int cma_iboe_join_multicast(struct rdma_id_private *id_priv,
 	if (cma_zero_addr(addr))
 		return -EINVAL;
 
-	work = kzalloc(sizeof *work, GFP_KERNEL);
-	if (!work)
-		return -ENOMEM;
-
 	gid_type = id_priv->cma_dev->default_gid_type[id_priv->id.port_num -
 		   rdma_start_port(id_priv->cma_dev->device)];
 	cma_iboe_set_mgid(addr, &ib.rec.mgid, gid_type);
@@ -4621,10 +4643,9 @@ static int cma_iboe_join_multicast(struct rdma_id_private *id_priv,
 
 	if (dev_addr->bound_dev_if)
 		ndev = dev_get_by_index(dev_addr->net, dev_addr->bound_dev_if);
-	if (!ndev) {
-		err = -ENODEV;
-		goto err_free;
-	}
+	if (!ndev)
+		return -ENODEV;
+
 	ib.rec.rate = iboe_get_rate(ndev);
 	ib.rec.hop_limit = 1;
 	ib.rec.mtu = iboe_get_mtu(ndev->mtu);
@@ -4642,24 +4663,15 @@ static int cma_iboe_join_multicast(struct rdma_id_private *id_priv,
 			err = -ENOTSUPP;
 	}
 	dev_put(ndev);
-	if (err || !ib.rec.mtu) {
-		if (!err)
-			err = -EINVAL;
-		goto err_free;
-	}
+	if (err || !ib.rec.mtu)
+		return err ?: -EINVAL;
+
 	rdma_ip2gid((struct sockaddr *)&id_priv->id.route.addr.src_addr,
 		    &ib.rec.port_gid);
-	work->id = id_priv;
-	INIT_WORK(&work->work, cma_work_handler);
-	cma_make_mc_event(0, id_priv, &ib, &work->event, mc);
-	/* Balances with cma_id_put() in cma_work_handler */
-	cma_id_get(id_priv);
-	queue_work(cma_wq, &work->work);
+	INIT_WORK(&mc->iboe_join.work, cma_iboe_join_work_handler);
+	cma_make_mc_event(0, id_priv, &ib, &mc->iboe_join.event, mc);
+	queue_work(cma_wq, &mc->iboe_join.work);
 	return 0;
-
-err_free:
-	kfree(work);
-	return err;
 }
 
 int rdma_join_multicast(struct rdma_cm_id *id, struct sockaddr *addr,