RDMA/core: Fix missing error check on dev_set_name()

If name memory allocation fails the name will be left empty and
device_add_one() will crash:

  kobject: (0000000004952746): attempted to be registered with empty name!
  WARNING: CPU: 0 PID: 329 at lib/kobject.c:234 kobject_add_internal+0x7ac/0x9a0 lib/kobject.c:234
  Kernel panic - not syncing: panic_on_warn set ...
  CPU: 0 PID: 329 Comm: syz-executor.5 Not tainted 5.6.0-rc2-syzkaller #0
  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
  Call Trace:
   __dump_stack lib/dump_stack.c:77 [inline]
   dump_stack+0x197/0x210 lib/dump_stack.c:118
   panic+0x2e3/0x75c kernel/panic.c:221
   __warn.cold+0x2f/0x3e kernel/panic.c:582
   report_bug+0x289/0x300 lib/bug.c:195
   fixup_bug arch/x86/kernel/traps.c:174 [inline]
   fixup_bug arch/x86/kernel/traps.c:169 [inline]
   do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:267
   do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:286
   invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
  RIP: 0010:kobject_add_internal+0x7ac/0x9a0 lib/kobject.c:234
  Code: 1a 98 ca f9 e9 f0 f8 ff ff 4c 89 f7 e8 6d 98 ca f9 e9 95 f9 ff ff e8 c3 f0 8b f9 4c 89 e6 48 c7 c7 a0 0e 1a 89 e8 e3 41 5c f9 <0f> 0b 41 bd ea ff ff ff e9 52 ff ff ff e8 a2 f0 8b f9 0f 0b e8 9b
  RSP: 0018:ffffc90005b27908 EFLAGS: 00010286
  RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
  RDX: 0000000000040000 RSI: ffffffff815eae46 RDI: fffff52000b64f13
  RBP: ffffc90005b27960 R08: ffff88805aeba480 R09: ffffed1015d06659
  R10: ffffed1015d06658 R11: ffff8880ae8332c7 R12: ffff8880a37fd000
  R13: 0000000000000000 R14: ffff888096691780 R15: 0000000000000001
   kobject_add_varg lib/kobject.c:390 [inline]
   kobject_add+0x150/0x1c0 lib/kobject.c:442
   device_add+0x3be/0x1d00 drivers/base/core.c:2412
   add_one_compat_dev drivers/infiniband/core/device.c:901 [inline]
   add_one_compat_dev+0x46a/0x7e0 drivers/infiniband/core/device.c:857
   rdma_dev_init_net+0x2eb/0x490 drivers/infiniband/core/device.c:1120
   ops_init+0xb3/0x420 net/core/net_namespace.c:137
   setup_net+0x2d5/0x8b0 net/core/net_namespace.c:327
   copy_net_ns+0x29e/0x5a0 net/core/net_namespace.c:468
   create_new_namespaces+0x403/0xb50 kernel/nsproxy.c:108
   unshare_nsproxy_namespaces+0xc2/0x200 kernel/nsproxy.c:229
   ksys_unshare+0x444/0x980 kernel/fork.c:2955
   __do_sys_unshare kernel/fork.c:3023 [inline]
   __se_sys_unshare kernel/fork.c:3021 [inline]
   __x64_sys_unshare+0x31/0x40 kernel/fork.c:3021
   do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

Link: https://lore.kernel.org/r/20200309193200.GA10633@ziepe.ca
Cc: stable@kernel.org
Fixes: 4e0f7b90 ("RDMA/core: Implement compat device/sysfs tree in net namespace")
Reported-by: syzbot+ab4dae63f7d310641ded@syzkaller.appspotmail.com
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/device.c

@@ -896,7 +896,9 @@ static int add_one_compat_dev(struct ib_device *device,
 	cdev->dev.parent = device->dev.parent;
 	rdma_init_coredev(cdev, device, read_pnet(&rnet->net));
 	cdev->dev.release = compatdev_release;
-	dev_set_name(&cdev->dev, "%s", dev_name(&device->dev));
+	ret = dev_set_name(&cdev->dev, "%s", dev_name(&device->dev));
+	if (ret)
+		goto add_err;
 
 	ret = device_add(&cdev->dev);
 	if (ret)