nfsd: fix lost nfserrno() call in nfsd_setattr()

There is a regression in
	208d0ac 2014-01-07 nfsd4: break only delegations when appropriate
which deletes an nfserrno() call in nfsd_setattr() (by accident,
probably), and NFSD becomes ignoring an error from VFS.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
vfs: atomic f_pos access in llseek()

Commit 9c225f2655e36a4 ("vfs: atomic f_pos accesses as per POSIX") changed
several system calls to use fdget_pos() instead of fdget(), but missed
sys_llseek().  Fix it.

Signed-off-by: Eric Biggers <ebiggers3@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: Don't let __fdget_pos() get FMODE_PATH files

Commit bd2a31d522344 ("get rid of fget_light()") introduced the
__fdget_pos() function, which returns the resulting file pointer and
fdput flags combined in an 'unsigned long'.  However, it also changed the
behavior to return files with FMODE_PATH set, which shouldn't happen
because read(), write(), lseek(), etc. aren't allowed on such files.
This commit restores the old behavior.

This regression actually had no effect on read() and write() since
FMODE_READ and FMODE_WRITE are not set on file descriptors opened with
O_PATH, but it did cause lseek() on a file descriptor opened with O_PATH
to fail with ESPIPE rather than EBADF.

Signed-off-by: Eric Biggers <ebiggers3@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
make prepend_name() work correctly when called with negative *buflen

In all callchains leading to prepend_name(), the value left in *buflen
is eventually discarded unused if prepend_name() has returned a negative.
So we are free to do what prepend() does, and subtract from *buflen
*before* checking for underflow (which turns into checking the sign
of subtraction result, of course).

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
rcuwalk: recheck mount_lock after mountpoint crossing attempts

We can get false negative from __lookup_mnt() if an unrelated vfsmount
gets moved.  In that case legitimize_mnt() is guaranteed to fail,
and we will fall back to non-RCU walk... unless we end up running
into a hard error on a filesystem object we wouldn't have reached
if not for that false negative.  IOW, delaying that check until
the end of pathname resolution is wrong - we should recheck right
after we attempt to cross the mountpoint.  We don't need to recheck
unless we see d_mountpoint() being true - in that case even if
we have just raced with mount/umount, we can simply go on as if
we'd come at the moment when the sucker wasn't a mountpoint; if we
run into a hard error as the result, it was a legitimate outcome.
__lookup_mnt() returning NULL is different in that respect, since
it might've happened due to operation on completely unrelated
mountpoint.

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull vfs fixes from Al Viro:
 "These four commits are obvious fixes (a couple of fdget_pos()-related
  ones from Eric Biggers, prepend_name() fix, missing checks for false
  negatives from __lookup_mnt() in fs/namei.c)"

For now I'm pulling just the four obvious fixes, there's another four
pending in Al's 'for-linus' branch wrt the mnt_hash list that were more
involved.

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  rcuwalk: recheck mount_lock after mountpoint crossing attempts
  make prepend_name() work correctly when called with negative *buflen
  vfs: Don't let __fdget_pos() get FMODE_PATH files
  vfs: atomic f_pos access in llseek()
Merge branch 'nfsd-next' of git://linux-nfs.org/~bfields/linux

Pull nfsd fix frm Bruce Fields:
 "J R Okajima sent this early and I was just slow to pass it along,
  apologies.  Fortunately it's a simple fix"

* 'nfsd-next' of git://linux-nfs.org/~bfields/linux:
  nfsd: fix lost nfserrno() call in nfsd_setattr()