1. 05 Feb, 2020 1 commit
    • Al Viro's avatar
      vfs: fix do_last() regression · 8d7a5100
      Al Viro authored
      commit 6404674a upstream.
      
      Brown paperbag time: fetching ->i_uid/->i_mode really should've been
      done from nd->inode.  I even suggested that, but the reason for that has
      slipped through the cracks and I went for dir->d_inode instead - made
      for more "obvious" patch.
      
      Analysis:
      
       - at the entry into do_last() and all the way to step_into(): dir (aka
         nd->path.dentry) is known not to have been freed; so's nd->inode and
         it's equal to dir->d_inode unless we are already doomed to -ECHILD.
         inode of the file to get opened is not known.
      
       - after step_into(): inode of the file to get opened is known; dir
         might be pointing to freed memory/be negative/etc.
      
       - at the call of may_create_in_sticky(): guaranteed to be out of RCU
         mode; inode of the file to get opened is known and pinned; dir might
         be garbage.
      
      The last was the reason for the original patch.  Except that at the
      do_last() entry we can be in RCU mode and it is possible that
      nd->path.dentry->d_inode has already changed under us.
      
      In that case we are going to fail with -ECHILD, but we need to be
      careful; nd->inode is pointing to valid struct inode and it's the same
      as nd->path.dentry->d_inode in "won't fail with -ECHILD" case, so we
      should use that.
      Reported-by: default avatar"Rantala, Tommi T. (Nokia - FI/Espoo)" <tommi.t.rantala@nokia.com>
      Reported-by: syzbot+190005201ced78a74ad6@syzkaller.appspotmail.com
      Wearing-brown-paperbag: Al Viro <viro@zeniv.linux.org.uk>
      Cc: stable@kernel.org
      Fixes: d0cb5018 ("do_last(): fetch directory ->i_mode and ->i_uid before it's too late")
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      8d7a5100
  2. 01 Feb, 2020 39 commits