[PATCH] sanitize locate_fd()

* 'file' argument is unused; lose it.
* move setting flags from the caller (dupfd()) to locate_fd();
  pass cloexec flag as new argument.  Note that files_fdtable()
  that used to be in dupfd() isn't needed in the place in
  locate_fd() where the moved code ends up - we know that ->file_lock
  hadn't been dropped since the last time we calculated fdt because
  we can get there only if expand_files() returns 0 and it doesn't
  drop/reacquire in that case.
* move getting/dropping ->file_lock into locate_fd().  Now the caller
  doesn't need to do anything with files_struct *files anymore and
  we can move that inside locate_fd() as well, killing the
  struct files_struct * argument.

At that point locate_fd() is extremely similar to get_unused_fd_flags()
and the next patches will merge those two.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 14 insertions, 26 deletions

diff --git a/fs/fcntl.c b/fs/fcntl.c
index e632da761fc1..3f3ac630ccde 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -55,14 +55,16 @@ static int get_close_on_exec(unsigned int fd)
  * file_lock held for write.
  */
 
-static int locate_fd(struct files_struct *files, 
-                            struct file *file, unsigned int orig_start)
+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);
+
         error = -EINVAL;
         if (orig_start >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
                 goto out;
@@ -97,42 +99,28 @@ repeat:
         if (error)
                 goto repeat;
 
-        /*
-         * We reacquired files_lock, so we are safe as long as
-         * we reacquire the fdtable pointer and use it while holding
-         * the lock, no one can free it during that time.
-         */
         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)
 {
-        struct files_struct * files = current->files;
-        struct fdtable *fdt;
-        int fd;
-
-        spin_lock(&files->file_lock);
-        fd = locate_fd(files, file, start);
-        if (fd >= 0) {
-                /* locate_fd() may have expanded fdtable, load the ptr */
-                fdt = files_fdtable(files);
-                FD_SET(fd, fdt->open_fds);
-                if (cloexec)
-                        FD_SET(fd, fdt->close_on_exec);
-                else
-                        FD_CLR(fd, fdt->close_on_exec);
-                spin_unlock(&files->file_lock);
+        int fd = locate_fd(start, cloexec);
+        if (fd >= 0)
                 fd_install(fd, file);
-        } else {
-                spin_unlock(&files->file_lock);
+        else
                 fput(file);
-        }
 
         return fd;
 }