convert cachestat(2)

fdput() can be transposed with copy_to_user()

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Al Viro

mm/filemap.c

@@ -4421,39 +4421,32 @@ SYSCALL_DEFINE4(cachestat, unsigned int, fd,
 		struct cachestat_range __user *, cstat_range,
 		struct cachestat __user *, cstat, unsigned int, flags)
 {
-	struct fd f = fdget(fd);
+	CLASS(fd, f)(fd);
 	struct address_space *mapping;
 	struct cachestat_range csr;
 	struct cachestat cs;
 	pgoff_t first_index, last_index;
 
-	if (!fd_file(f))
+	if (fd_empty(f))
 		return -EBADF;
 
 	if (copy_from_user(&csr, cstat_range,
-			sizeof(struct cachestat_range))) {
-		fdput(f);
+			sizeof(struct cachestat_range)))
 		return -EFAULT;
-	}
 
 	/* hugetlbfs is not supported */
-	if (is_file_hugepages(fd_file(f))) {
-		fdput(f);
+	if (is_file_hugepages(fd_file(f)))
 		return -EOPNOTSUPP;
-	}
 
-	if (flags != 0) {
-		fdput(f);
+	if (flags != 0)
 		return -EINVAL;
-	}
 
 	first_index = csr.off >> PAGE_SHIFT;
 	last_index =
 		csr.len == 0 ? ULONG_MAX : (csr.off + csr.len - 1) >> PAGE_SHIFT;
 	memset(&cs, 0, sizeof(struct cachestat));
 	mapping = fd_file(f)->f_mapping;
 	filemap_cachestat(mapping, first_index, last_index, &cs);
-	fdput(f);
 
 	if (copy_to_user(cstat, &cs, sizeof(struct cachestat)))
 		return -EFAULT;