[PATCH][next] fs: Annotate struct file_handle with __counted_by() and use struct_size()

["Gustavo A. R. Silva" <gustavoars@kernel.org>]

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

While there, use struct_size() helper, instead of the open-coded
version.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 fs/fhandle.c       | 8 ++++----
 include/linux/fs.h | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/fhandle.c b/fs/fhandle.c
index 57a12614addf..53ed54711cd2 100644
--- a/fs/fhandle.c
+++ b/fs/fhandle.c
@@ -36,7 +36,7 @@ static long do_sys_name_to_handle(const struct path *path,
 	if (f_handle.handle_bytes > MAX_HANDLE_SZ)
 		return -EINVAL;
 
-	handle = kzalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
+	handle = kzalloc(struct_size(handle, f_handle, f_handle.handle_bytes),
 			 GFP_KERNEL);
 	if (!handle)
 		return -ENOMEM;
@@ -71,7 +71,7 @@ static long do_sys_name_to_handle(const struct path *path,
 	/* copy the mount id */
 	if (put_user(real_mount(path->mnt)->mnt_id, mnt_id) ||
 	    copy_to_user(ufh, handle,
-			 sizeof(struct file_handle) + handle_bytes))
+			 struct_size(handle, f_handle, handle_bytes)))
 		retval = -EFAULT;
 	kfree(handle);
 	return retval;
@@ -192,7 +192,7 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
 		retval = -EINVAL;
 		goto out_err;
 	}
-	handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
+	handle = kmalloc(struct_size(handle, f_handle, f_handle.handle_bytes),
 			 GFP_KERNEL);
 	if (!handle) {
 		retval = -ENOMEM;
@@ -202,7 +202,7 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
 	*handle = f_handle;
 	if (copy_from_user(&handle->f_handle,
 			   &ufh->f_handle,
-			   f_handle.handle_bytes)) {
+			   struct_size(ufh, f_handle, f_handle.handle_bytes))) {
 		retval = -EFAULT;
 		goto out_handle;
 	}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 034f0c918eea..1540e28d10d7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1033,7 +1033,7 @@ struct file_handle {
 	__u32 handle_bytes;
 	int handle_type;
 	/* file identifier */
-	unsigned char f_handle[];
+	unsigned char f_handle[] __counted_by(handle_bytes);
 };
 
 static inline struct file *get_file(struct file *f)
-- 
2.34.1