IB/core: uverbs copy to struct or zero helper

Add a helper to zero fill fields before copying data to
UVERBS_ATTR_STRUCT.

As UVERBS_ATTR_STRUCT can be used as an extensible struct, we want to make
sure that if the user supplies us with a struct that has new fields that
we are not aware of, we return them zeroed to the user.

This helper should be used when using UVERBS_ATTR_STRUCT for an extendable
data structure and there is a need to make sure that extended members of
the struct, that the kernel doesn't handle, are returned zeroed to the
user. This is needed due to the fact that UVERBS_ATTR_STRUCT allows
non-zero values for members after 'last' member.

Signed-off-by: Michael Guralnik <michaelgur@mellanox.com>
Reviewed-by: Majd Dibbiny <majd@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/infiniband/core/uverbs_ioctl.c b/drivers/infiniband/core/uverbs_ioctl.c
index 3cc46447240e..8c81ff698052 100644
--- a/drivers/infiniband/core/uverbs_ioctl.c
+++ b/drivers/infiniband/core/uverbs_ioctl.c
@@ -751,3 +751,14 @@ int _uverbs_get_const(s64 *to, const struct uverbs_attr_bundle *attrs_bundle,
 	return 0;
 }
 EXPORT_SYMBOL(_uverbs_get_const);
+
+int uverbs_copy_to_struct_or_zero(const struct uverbs_attr_bundle *bundle,
+				  size_t idx, const void *from, size_t size)
+{
+	const struct uverbs_attr *attr = uverbs_attr_get(bundle, idx);
+
+	if (clear_user(u64_to_user_ptr(attr->ptr_attr.data),
+		       attr->ptr_attr.len))
+		return -EFAULT;
+	return uverbs_copy_to(bundle, idx, from, size);
+}