misc: vmw_vmci: fix kernel info-leak by initializing dbells in vmci_ctx_get_chkpt_doorbells()

A kernel-infoleak was reported by syzbot, which was caused because
dbells was left uninitialized.
Using kzalloc() instead of kmalloc() fixes this issue.

Reported-by: syzbot+a79e17c39564bedf0930@syzkaller.appspotmail.com
Tested-by: syzbot+a79e17c39564bedf0930@syzkaller.appspotmail.com
Signed-off-by: NAnant Thazhemadam <anant.thazhemadam@gmail.com>
Link: https://lore.kernel.org/r/20201122224534.333471-1-anant.thazhemadam@gmail.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/vmw_vmci/vmci_context.c

@@ -743,7 +743,7 @@ static int vmci_ctx_get_chkpt_doorbells(struct vmci_ctx *context,
 			return VMCI_ERROR_MORE_DATA;
 		}
 
-		dbells = kmalloc(data_size, GFP_ATOMIC);
+		dbells = kzalloc(data_size, GFP_ATOMIC);
 		if (!dbells)
 			return VMCI_ERROR_NO_MEM;