tracing: Prevent bad count for tracing_cpumask_write

commit 98feccb upstream.

If a large count is provided, it will trigger a warning in bitmap_parse_user.
Also check zero for it.

Cc: [email protected]
Fixes: 9e01c1b ("cpumask: convert kernel trace functions")
Link: https://lore.kernel.org/[email protected]
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=0aecfd34fb878546f3fd
Tested-by: [email protected]
Signed-off-by: Lizhi Xu <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Lizhi Xu

kernel/trace/trace.c

@@ -5331,6 +5331,9 @@ tracing_cpumask_write(struct file *filp, const char __user *ubuf,
 	cpumask_var_t tracing_cpumask_new;
 	int err;
 
+	if (count == 0 || count > KMALLOC_MAX_SIZE)
+		return -EINVAL;
+
 	if (!zalloc_cpumask_var(&tracing_cpumask_new, GFP_KERNEL))
 		return -ENOMEM;