RDMA/uverbs: Avoid -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
ready to enable it globally.

There are currently a couple of objects (`alloc_head` and `bundle`) in
`struct bundle_priv` that contain a couple of flexible structures:

struct bundle_priv {
/* Must be first */
struct bundle_alloc_head alloc_head;

...

/*
* Must be last. bundle ends in a flex array which overlaps
* internal_buffer.
*/
struct uverbs_attr_bundle bundle;
u64 internal_buffer[32];
};

So, in order to avoid ending up with a couple of flexible-array members
in the middle of a struct, we use the `struct_group_tagged()` helper to
separate the flexible array from the rest of the members in the flexible
structures:

struct uverbs_attr_bundle {
struct_group_tagged(uverbs_attr_bundle_hdr, hdr,
... the rest of the members
);
struct uverbs_attr attrs[];
};

With the change described above, we now declare objects of the type of
the tagged struct without embedding flexible arrays in the middle of
another struct:

struct bundle_priv {
/* Must be first */
struct bundle_alloc_head_hdr alloc_head;

...

struct uverbs_attr_bundle_hdr bundle;
u64 internal_buffer[32];
};

We also use `container_of()` whenever we need to retrieve a pointer
to the flexible structures.

Notice that the `bundle_size` computed in `uapi_compute_bundle_size()`
remains the same.

So, with these changes, fix the following warnings:

drivers/infiniband/core/uverbs_ioctl.c:45:34: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
45 | struct bundle_alloc_head alloc_head;
| ^~~~~~~~~~
drivers/infiniband/core/uverbs_ioctl.c:67:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
67 | struct uverbs_attr_bundle bundle;
| ^~~~~~

Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Link: https://lore.kernel.org/r/ZeIgeZ5Sb0IZTOyt@neat
Reviewed-by: Kees Cook <[e-mail]>
Signed-off-by: Leon Romanovsky <[e-mail]>

drivers/infiniband/core/uverbs_ioctl.c

···
 #include "uverbs.h"
 
 struct bundle_alloc_head {
-	struct bundle_alloc_head *next;
+	struct_group_tagged(bundle_alloc_head_hdr, hdr,
+		struct bundle_alloc_head *next;
+	);
 	u8 data[];
 };
 
 struct bundle_priv {
 	/* Must be first */
-	struct bundle_alloc_head alloc_head;
+	struct bundle_alloc_head_hdr alloc_head;
 	struct bundle_alloc_head *allocated_mem;
 	size_t internal_avail;
 	size_t internal_used;
···
 	 * Must be last. bundle ends in a flex array which overlaps
 	 * internal_buffer.
 	 */
-	struct uverbs_attr_bundle bundle;
+	struct uverbs_attr_bundle_hdr bundle;
 	u64 internal_buffer[32];
 };
 
···
 			      unsigned int num_attrs)
 {
 	struct bundle_priv *pbundle;
+	struct uverbs_attr_bundle *bundle;
 	size_t bundle_size =
 		offsetof(struct bundle_priv, internal_buffer) +
-		sizeof(*pbundle->bundle.attrs) * method_elm->key_bitmap_len +
+		sizeof(*bundle->attrs) * method_elm->key_bitmap_len +
 		sizeof(*pbundle->uattrs) * num_attrs;
 
 	method_elm->use_stack = bundle_size <= sizeof(*pbundle);
···
 			     gfp_t flags)
 {
 	struct bundle_priv *pbundle =
-		container_of(bundle, struct bundle_priv, bundle);
+		container_of(&bundle->hdr, struct bundle_priv, bundle);
 	size_t new_used;
 	void *res;
 
···
 			     const struct uverbs_attr *attr)
 {
 	struct bundle_priv *pbundle =
-		container_of(bundle, struct bundle_priv, bundle);
+		container_of(&bundle->hdr, struct bundle_priv, bundle);
 	u16 flags;
 
 	flags = pbundle->uattrs[attr->ptr_attr.uattr_idx].flags |
···
 				     struct ib_uverbs_attr *uattr,
 				     u32 attr_bkey)
 {
+	struct uverbs_attr_bundle *bundle =
+		container_of(&pbundle->bundle, struct uverbs_attr_bundle, hdr);
 	const struct uverbs_attr_spec *spec = &attr_uapi->spec;
 	size_t array_len;
 	u32 *idr_vals;
···
 		return -EINVAL;
 
 	attr->uobjects =
-		uverbs_alloc(&pbundle->bundle,
+		uverbs_alloc(bundle,
 			     array_size(array_len, sizeof(*attr->uobjects)));
 	if (IS_ERR(attr->uobjects))
 		return PTR_ERR(attr->uobjects);
···
 	for (i = 0; i != array_len; i++) {
 		attr->uobjects[i] = uverbs_get_uobject_from_file(
 			spec->u2.objs_arr.obj_type, spec->u2.objs_arr.access,
-			idr_vals[i], &pbundle->bundle);
+			idr_vals[i], bundle);
 		if (IS_ERR(attr->uobjects[i])) {
 			ret = PTR_ERR(attr->uobjects[i]);
 			break;
···
 			       struct ib_uverbs_attr *uattr, u32 attr_bkey)
 {
 	const struct uverbs_attr_spec *spec = &attr_uapi->spec;
-	struct uverbs_attr *e = &pbundle->bundle.attrs[attr_bkey];
+	struct uverbs_attr_bundle *bundle =
+		container_of(&pbundle->bundle, struct uverbs_attr_bundle, hdr);
+	struct uverbs_attr *e = &bundle->attrs[attr_bkey];
 	const struct uverbs_attr_spec *val_spec = spec;
 	struct uverbs_obj_attr *o_attr;
 
···
 		if (val_spec->alloc_and_copy && !uverbs_attr_ptr_is_inline(e)) {
 			void *p;
 
-			p = uverbs_alloc(&pbundle->bundle, uattr->len);
+			p = uverbs_alloc(bundle, uattr->len);
 			if (IS_ERR(p))
 				return PTR_ERR(p);
 
···
 		 */
 		o_attr->uobject = uverbs_get_uobject_from_file(
 			spec->u.obj.obj_type, spec->u.obj.access,
-			uattr->data_s64, &pbundle->bundle);
+			uattr->data_s64, bundle);
 		if (IS_ERR(o_attr->uobject))
 			return PTR_ERR(o_attr->uobject);
 		__set_bit(attr_bkey, pbundle->uobj_finalize);
···
 				unsigned int num_attrs)
 {
 	int (*handler)(struct uverbs_attr_bundle *attrs);
+	struct uverbs_attr_bundle *bundle =
+		container_of(&pbundle->bundle, struct uverbs_attr_bundle, hdr);
 	size_t uattrs_size = array_size(sizeof(*pbundle->uattrs), num_attrs);
 	unsigned int destroy_bkey = pbundle->method_elm->destroy_bkey;
 	unsigned int i;
···
 	if (!handler)
 		return -EIO;
 
-	pbundle->uattrs = uverbs_alloc(&pbundle->bundle, uattrs_size);
+	pbundle->uattrs = uverbs_alloc(bundle, uattrs_size);
 	if (IS_ERR(pbundle->uattrs))
 		return PTR_ERR(pbundle->uattrs);
 	if (copy_from_user(pbundle->uattrs, pbundle->user_attrs, uattrs_size))
···
 		return -EINVAL;
 
 	if (pbundle->method_elm->has_udata)
-		uverbs_fill_udata(&pbundle->bundle,
-				  &pbundle->bundle.driver_udata,
+		uverbs_fill_udata(bundle, &pbundle->bundle.driver_udata,
 				  UVERBS_ATTR_UHW_IN, UVERBS_ATTR_UHW_OUT);
 	else
 		pbundle->bundle.driver_udata = (struct ib_udata){};
 
 	if (destroy_bkey != UVERBS_API_ATTR_BKEY_LEN) {
-		struct uverbs_obj_attr *destroy_attr =
-			&pbundle->bundle.attrs[destroy_bkey].obj_attr;
+		struct uverbs_obj_attr *destroy_attr = &bundle->attrs[destroy_bkey].obj_attr;
 
-		ret = uobj_destroy(destroy_attr->uobject, &pbundle->bundle);
+		ret = uobj_destroy(destroy_attr->uobject, bundle);
 		if (ret)
 			return ret;
 		__clear_bit(destroy_bkey, pbundle->uobj_finalize);
 
-		ret = handler(&pbundle->bundle);
+		ret = handler(bundle);
 		uobj_put_destroy(destroy_attr->uobject);
 	} else {
-		ret = handler(&pbundle->bundle);
+		ret = handler(bundle);
 	}
 
 	/*
···
 	 */
 	if (!ret && pbundle->method_elm->has_udata) {
 		const struct uverbs_attr *attr =
-			uverbs_attr_get(&pbundle->bundle, UVERBS_ATTR_UHW_OUT);
+			uverbs_attr_get(bundle, UVERBS_ATTR_UHW_OUT);
 
 		if (!IS_ERR(attr))
-			ret = uverbs_set_output(&pbundle->bundle, attr);
+			ret = uverbs_set_output(bundle, attr);
 	}
 
 	/*
···
 static void bundle_destroy(struct bundle_priv *pbundle, bool commit)
 {
 	unsigned int key_bitmap_len = pbundle->method_elm->key_bitmap_len;
+	struct uverbs_attr_bundle *bundle =
+		container_of(&pbundle->bundle, struct uverbs_attr_bundle, hdr);
 	struct bundle_alloc_head *memblock;
 	unsigned int i;
 
···
 	i = -1;
 	while ((i = find_next_bit(pbundle->uobj_finalize, key_bitmap_len,
 				  i + 1)) < key_bitmap_len) {
-		struct uverbs_attr *attr = &pbundle->bundle.attrs[i];
+		struct uverbs_attr *attr = &bundle->attrs[i];
 
 		uverbs_finalize_object(
 			attr->obj_attr.uobject,
 			attr->obj_attr.attr_elm->spec.u.obj.access,
 			test_bit(i, pbundle->uobj_hw_obj_valid),
-			commit,
-			&pbundle->bundle);
+			commit, bundle);
 	}
 
 	i = -1;
 	while ((i = find_next_bit(pbundle->spec_finalize, key_bitmap_len,
 				  i + 1)) < key_bitmap_len) {
-		struct uverbs_attr *attr = &pbundle->bundle.attrs[i];
+		struct uverbs_attr *attr = &bundle->attrs[i];
 		const struct uverbs_api_attr *attr_uapi;
 		void __rcu **slot;
 
···
 
 		if (attr_uapi->spec.type == UVERBS_ATTR_TYPE_IDRS_ARRAY) {
 			uverbs_free_idrs_array(attr_uapi, &attr->objs_arr_attr,
-					       commit, &pbundle->bundle);
+					       commit, bundle);
 		}
 	}
 
···
 			method_elm->bundle_size -
 			offsetof(struct bundle_priv, internal_buffer);
 		pbundle->alloc_head.next = NULL;
-		pbundle->allocated_mem = &pbundle->alloc_head;
+		pbundle->allocated_mem = container_of(&pbundle->alloc_head,
+						struct bundle_alloc_head, hdr);
 	} else {
 		pbundle = &onstack;
 		pbundle->internal_avail = sizeof(pbundle->internal_buffer);
···
 	pbundle->user_attrs = user_attrs;
 
 	pbundle->internal_used = ALIGN(pbundle->method_elm->key_bitmap_len *
-					       sizeof(*pbundle->bundle.attrs),
-				       sizeof(*pbundle->internal_buffer));
+					       sizeof(*container_of(&pbundle->bundle,
+							struct uverbs_attr_bundle, hdr)->attrs),
+					       sizeof(*pbundle->internal_buffer));
 	memset(pbundle->bundle.attr_present, 0,
 	       sizeof(pbundle->bundle.attr_present));
 	memset(pbundle->uobj_finalize, 0, sizeof(pbundle->uobj_finalize));
···
 		       unsigned int attr_out)
 {
 	struct bundle_priv *pbundle =
-		container_of(bundle, struct bundle_priv, bundle);
+		container_of(&bundle->hdr, struct bundle_priv, bundle);
+	struct uverbs_attr_bundle *bundle_aux =
+		container_of(&pbundle->bundle, struct uverbs_attr_bundle, hdr);
 	const struct uverbs_attr *in =
-		uverbs_attr_get(&pbundle->bundle, attr_in);
+		uverbs_attr_get(bundle_aux, attr_in);
 	const struct uverbs_attr *out =
-		uverbs_attr_get(&pbundle->bundle, attr_out);
+		uverbs_attr_get(bundle_aux, attr_out);
 
 	if (!IS_ERR(in)) {
 		udata->inlen = in->ptr_attr.len;
···
 				 u16 idx)
 {
 	struct bundle_priv *pbundle =
-		container_of(bundle, struct bundle_priv, bundle);
+		container_of(&bundle->hdr, struct bundle_priv, bundle);
 
 	__set_bit(uapi_bkey_attr(uapi_key_attr(idx)),
 		  pbundle->uobj_hw_obj_valid);

include/rdma/uverbs_ioctl.h

···
 };
 
 struct uverbs_attr_bundle {
-	struct ib_udata driver_udata;
-	struct ib_udata ucore;
-	struct ib_uverbs_file *ufile;
-	struct ib_ucontext *context;
-	struct ib_uobject *uobject;
-	DECLARE_BITMAP(attr_present, UVERBS_API_ATTR_BKEY_LEN);
+	struct_group_tagged(uverbs_attr_bundle_hdr, hdr,
+		struct ib_udata driver_udata;
+		struct ib_udata ucore;
+		struct ib_uverbs_file *ufile;
+		struct ib_ucontext *context;
+		struct ib_uobject *uobject;
+		DECLARE_BITMAP(attr_present, UVERBS_API_ATTR_BKEY_LEN);
+	);
 	struct uverbs_attr attrs[];
 };