IB/core: Add ib_is_udata_cleared

Extending core and vendor verb commands require us to check that the
unknown part of the user's given command is all zeros.
Adding ib_is_udata_cleared in order to do so.
Signed-off-by: Matan Barak <matanb@mellanox.com>
Reviewed-by: Haggai Eran <haggaie@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

include/rdma/ib_verbs.h

@@ -53,6 +53,8 @@
 #include <uapi/linux/if_ether.h>
 #include <net/ipv6.h>
 #include <net/ip.h>
+#include <linux/string.h>
+#include <linux/slab.h>
 
 #include <linux/atomic.h>
 #include <linux/mmu_notifier.h>
@@ -1922,6 +1924,31 @@ static inline int ib_copy_to_udata(struct ib_udata *udata, void *src, size_t len
 	return copy_to_user(udata->outbuf, src, len) ? -EFAULT : 0;
 }
 
+static inline bool ib_is_udata_cleared(struct ib_udata *udata,
+				       size_t offset,
+				       size_t len)
+{
+	const void __user *p = udata->inbuf + offset;
+	bool ret = false;
+	u8 *buf;
+
+	if (len > USHRT_MAX)
+		return false;
+
+	buf = kmalloc(len, GFP_KERNEL);
+	if (!buf)
+		return false;
+
+	if (copy_from_user(buf, p, len))
+		goto free;
+
+	ret = !memchr_inv(buf, 0, len);
+
+free:
+	kfree(buf);
+	return ret;
+}
+
 /**
  * ib_modify_qp_is_ok - Check that the supplied attribute mask
  * contains all required attributes and no attributes not allowed for