Anon wrote: > I'm not quite sure whom I should send this report to but recently > I've noticed that I can remove files which owner is root and that > have access mode set as 644 (see example below).
The permissions on the file are not relevant. It is only permissions on the directory that matter. You are not actually doing anything to the file when you remove it from the directory containing it. Instead you are removing the file's entry from the directory containing it. The file is not modified. The directory is modified. Before removing the directory contains an entry. You remove the entry from the directory. The directory is modified and you must have write permission for the directory. Permissions on the file are not involved. If you have a file and link it into two different directories and then remove the file from one of the two you will note that the file itself is not modified. Only the directory is modifed. That is why removing files do not modify the file itself. Write permission on the file is not needed since the file is not modified. Only write permission to the directory because only the directory is modified. The filesystem maintains the link count for files. You might typically see a "1" in the directory listing for the link count for the file. If you link a file into another directory then the link count will be increased by one for ever additional directory entry. Removing the entry from the directory decrements the link count by one. When the file entry is removed from the very last directory holding a link to it the link count will be reduced to zero. When the link count is reduced to zero then the filesystem will garbage collect the storage block space of the file. Removing the file doesn't actually delete the file but reducing the link count to zero causes the filesystem to garbage collect it. Note that open file descriptors to a file keep the link count to be non-zero but are not displayed in the directory listing. > I've tried to reproduce it with another user but everything works as > it should, i.e. I couldn't remove files which owner is root, so I > assume that maybe there was a problem with amd64 testing netinstall > iso which I installed my system from. Undoubted the directory permissions in this other example prevent you from removing that file. Note that /tmp has the 't' bit set so that you cannot remove files that you do not own. This is a security feature. Bob
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