userfaultfd: convert to use anon_inode_getfd()

Nothing actually calls userfaultfd_file_create() besides the
userfaultfd() system call itself.  So simplify things by folding it into
the system call and using anon_inode_getfd() instead of
anon_inode_getfile().  Do the same in resolve_userfault_fork() as well.

This removes over 50 lines with no change in functionality.

Link: http://lkml.kernel.org/r/20171229212403.22800-1-ebiggers3@gmail.com
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index a9d0ddc12aced408107cd0fe384f5cc51cfffd75..87a13a7c8270bce8428f3d89fa3fb04f08e49f63 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -988,24 +988,14 @@ static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
                                  struct uffd_msg *msg)
 {
        int fd;
-       struct file *file;
-       unsigned int flags = new->flags & UFFD_SHARED_FCNTL_FLAGS;
 
-       fd = get_unused_fd_flags(flags);
+       fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, new,
+                             O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS));
        if (fd < 0)
                return fd;
 
-       file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, new,
-                                 O_RDWR | flags);
-       if (IS_ERR(file)) {
-               put_unused_fd(fd);
-               return PTR_ERR(file);
-       }
-
-       fd_install(fd, file);
        msg->arg.reserved.reserved1 = 0;
        msg->arg.fork.ufd = fd;
-
        return 0;
 }
 
@@ -1887,24 +1877,10 @@ static void init_once_userfaultfd_ctx(void *mem)
        seqcount_init(&ctx->refile_seq);
 }
 
-/**
- * userfaultfd_file_create - Creates a userfaultfd file pointer.
- * @flags: Flags for the userfaultfd file.
- *
- * This function creates a userfaultfd file pointer, w/out installing
- * it into the fd table. This is useful when the userfaultfd file is
- * used during the initialization of data structures that require
- * extra setup after the userfaultfd creation. So the userfaultfd
- * creation is split into the file pointer creation phase, and the
- * file descriptor installation phase.  In this way races with
- * userspace closing the newly installed file descriptor can be
- * avoided.  Returns a userfaultfd file pointer, or a proper error
- * pointer.
- */
-static struct file *userfaultfd_file_create(int flags)
+SYSCALL_DEFINE1(userfaultfd, int, flags)
 {
-       struct file *file;
        struct userfaultfd_ctx *ctx;
+       int fd;
 
        BUG_ON(!current->mm);
 
@@ -1912,14 +1888,12 @@ static struct file *userfaultfd_file_create(int flags)
        BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
        BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
 
-       file = ERR_PTR(-EINVAL);
        if (flags & ~UFFD_SHARED_FCNTL_FLAGS)
-               goto out;
+               return -EINVAL;
 
-       file = ERR_PTR(-ENOMEM);
        ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
        if (!ctx)
-               goto out;
+               return -ENOMEM;
 
        atomic_set(&ctx->refcount, 1);
        ctx->flags = flags;
@@ -1930,39 +1904,13 @@ static struct file *userfaultfd_file_create(int flags)
        /* prevent the mm struct to be freed */
        mmgrab(ctx->mm);
 
-       file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
-                                 O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
-       if (IS_ERR(file)) {
+       fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, ctx,
+                             O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
+       if (fd < 0) {
                mmdrop(ctx->mm);
                kmem_cache_free(userfaultfd_ctx_cachep, ctx);
        }
-out:
-       return file;
-}
-
-SYSCALL_DEFINE1(userfaultfd, int, flags)
-{
-       int fd, error;
-       struct file *file;
-
-       error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS);
-       if (error < 0)
-               return error;
-       fd = error;
-
-       file = userfaultfd_file_create(flags);
-       if (IS_ERR(file)) {
-               error = PTR_ERR(file);
-               goto err_put_unused_fd;
-       }
-       fd_install(fd, file);
-
        return fd;
-
-err_put_unused_fd:
-       put_unused_fd(fd);
-
-       return error;
 }
 
 static int __init userfaultfd_init(void)