ntb: fix possible NULL dereference

kmalloc can fail and we should check for NULL before using the pointer
returned by kmalloc.
Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

drivers/ntb/test/ntb_perf.c

@@ -550,6 +550,8 @@ static ssize_t debugfs_run_read(struct file *filp, char __user *ubuf,
 		return 0;
 
 	buf = kmalloc(64, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
 	out_offset = snprintf(buf, 64, "%d\n", perf->run);
 	ret = simple_read_from_buffer(ubuf, count, offp, buf, out_offset);
 	kfree(buf);