1 files changed, 41 insertions, 99 deletions

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 61d625136813..ac4f7db9f134 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -49,73 +49,6 @@ static int get_close_on_exec(unsigned int fd)
         return res;
 }
 
-/*
- * locate_fd finds a free file descriptor in the open_fds fdset,
- * expanding the fd arrays if necessary.  Must be called with the
- * file_lock held for write.
- */
-
-static int locate_fd(unsigned int orig_start, int cloexec)
-{
-        struct files_struct *files = current->files;
-        unsigned int newfd;
-        unsigned int start;
-        int error;
-        struct fdtable *fdt;
-
-        spin_lock(&files->file_lock);
-repeat:
-        fdt = files_fdtable(files);
-        /*
-         * Someone might have closed fd's in the range
-         * orig_start..fdt->next_fd
-         */
-        start = orig_start;
-        if (start < files->next_fd)
-                start = files->next_fd;
-
-        newfd = start;
-        if (start < fdt->max_fds)
-                newfd = find_next_zero_bit(fdt->open_fds->fds_bits,
-                                           fdt->max_fds, start);
-
-        error = expand_files(files, newfd);
-        if (error < 0)
-                goto out;
-
-        /*
-         * If we needed to expand the fs array we
-         * might have blocked - try again.
-         */
-        if (error)
-                goto repeat;
-
-        if (start <= files->next_fd)
-                files->next_fd = newfd + 1;
-
-        FD_SET(newfd, fdt->open_fds);
-        if (cloexec)
-                FD_SET(newfd, fdt->close_on_exec);
-        else
-                FD_CLR(newfd, fdt->close_on_exec);
-        error = newfd;
-
-out:
-        spin_unlock(&files->file_lock);
-        return error;
-}
-
-static int dupfd(struct file *file, unsigned int start, int cloexec)
-{
-        int fd = locate_fd(start, cloexec);
-        if (fd >= 0)
-                fd_install(fd, file);
-        else
-                fput(file);
-
-        return fd;
-}
-
 asmlinkage long sys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
 {
         int err = -EBADF;
@@ -130,31 +63,35 @@ asmlinkage long sys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
                 return -EINVAL;
 
         spin_lock(&files->file_lock);
-        if (!(file = fcheck(oldfd)))
-                goto out_unlock;
-        get_file(file);                 /* We are now finished with oldfd */
-
         err = expand_files(files, newfd);
+        file = fcheck(oldfd);
+        if (unlikely(!file))
+                goto Ebadf;
         if (unlikely(err < 0)) {
                 if (err == -EMFILE)
-                        err = -EBADF;
-                goto out_fput;
+                        goto Ebadf;
+                goto out_unlock;
         }
-
-        /* To avoid races with open() and dup(), we will mark the fd as
-         * in-use in the open-file bitmap throughout the entire dup2()
-         * process.  This is quite safe: do_close() uses the fd array
-         * entry, not the bitmap, to decide what work needs to be
-         * done.  --sct */
-        /* Doesn't work. open() might be there first. --AV */
-
-        /* Yes. It's a race. In user space. Nothing sane to do */
+        /*
+         * We need to detect attempts to do dup2() over allocated but still
+         * not finished descriptor.  NB: OpenBSD avoids that at the price of
+         * extra work in their equivalent of fget() - they insert struct
+         * file immediately after grabbing descriptor, mark it larval if
+         * more work (e.g. actual opening) is needed and make sure that
+         * fget() treats larval files as absent.  Potentially interesting,
+         * but while extra work in fget() is trivial, locking implications
+         * and amount of surgery on open()-related paths in VFS are not.
+         * FreeBSD fails with -EBADF in the same situation, NetBSD "solution"
+         * deadlocks in rather amusing ways, AFAICS.  All of that is out of
+         * scope of POSIX or SUS, since neither considers shared descriptor
+         * tables and this condition does not arise without those.
+         */
         err = -EBUSY;
         fdt = files_fdtable(files);
         tofree = fdt->fd[newfd];
         if (!tofree && FD_ISSET(newfd, fdt->open_fds))
-                goto out_fput;
-
+                goto out_unlock;
+        get_file(file);
         rcu_assign_pointer(fdt->fd[newfd], file);
         FD_SET(newfd, fdt->open_fds);
         if (flags & O_CLOEXEC)
@@ -165,17 +102,14 @@ asmlinkage long sys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
 
         if (tofree)
                 filp_close(tofree, files);
-        err = newfd;
-out:
-        return err;
-out_unlock:
-        spin_unlock(&files->file_lock);
-        goto out;
 
-out_fput:
+        return newfd;
+
+Ebadf:
+        err = -EBADF;
+out_unlock:
         spin_unlock(&files->file_lock);
-        fput(file);
-        goto out;
+        return err;
 }
 
 asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd)
@@ -194,10 +128,15 @@ asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd)
 asmlinkage long sys_dup(unsigned int fildes)
 {
         int ret = -EBADF;
-        struct file * file = fget(fildes);
-
-        if (file)
-                ret = dupfd(file, 0, 0);
+        struct file *file = fget(fildes);
+
+        if (file) {
+                ret = get_unused_fd();
+                if (ret >= 0)
+                        fd_install(ret, file);
+                else
+                        fput(file);
+        }
         return ret;
 }
 
@@ -322,8 +261,11 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
         case F_DUPFD_CLOEXEC:
                 if (arg >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
                         break;
-                get_file(filp);
-                err = dupfd(filp, arg, cmd == F_DUPFD_CLOEXEC);
+                err = alloc_fd(arg, cmd == F_DUPFD_CLOEXEC ? O_CLOEXEC : 0);
+                if (err >= 0) {
+                        get_file(filp);
+                        fd_install(err, filp);
+                }
                 break;
         case F_GETFD:
                 err = get_close_on_exec(fd) ? FD_CLOEXEC : 0;