vfs: make O_PATH file descriptors usable for 'fchdir()'

We already use them for openat() and friends, but fchdir() also wants to
be able to use O_PATH file descriptors.  This should make it comparable
to the O_SEARCH of Solaris.  In particular, O_PATH allows you to access
(not-quite-open) a directory you don't have read persmission to, only
execute permission.

Noticed during development of multithread support for ksh93.

Reported-by: ольга крыжановская <olga.kryzhanovska@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@kernel.org    # O_PATH introduced in 3.0+
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/open.c b/fs/open.c
index d6c79a0..1540632 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -397,10 +397,10 @@ SYSCALL_DEFINE1(fchdir, unsigned int, fd)
 {
        struct file *file;
        struct inode *inode;
-       int error;
+       int error, fput_needed;
 
        error = -EBADF;
-       file = fget(fd);
+       file = fget_raw_light(fd, &fput_needed);
        if (!file)
                goto out;
 
@@ -414,7 +414,7 @@ SYSCALL_DEFINE1(fchdir, unsigned int, fd)
        if (!error)
                set_fs_pwd(current->fs, &file->f_path);
 out_putf:
-       fput(file);
+       fput_light(file, fput_needed);
 out:
        return error;
 }