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    SubjectRe: [RFC/PATCH] revoke/frevoke system calls
    On 2006.07.20 23:02:53 +0300, Kari Hurtta wrote:
    > Pekka J Enberg <penberg@cs.Helsinki.FI> writes in
    > gmane.linux.file-systems,gmane.linux.kernel:
    >
    > > From: Pekka Enberg <penberg@cs.helsinki.fi>
    > >
    > > This patch implements the revoke(2) and frevoke(2) system calls for all
    > > types of files. We revoke files in two passes: first we scan all open
    > > files that refer to the inode and substitute the struct file pointer in fd
    > > table with NULL causing all subsequent operations on that fd to fail.
    > > After we have done that to all file descriptors, we close the files and
    > > take down mmaps.
    > >
    > > Note that now we need to unconditionally do fput/fget in sys_write and
    > > sys_read because they race with do_revoke.
    > >
    > > Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
    >
    > What permissions is needed revoke access of other users open
    > files ?
    >
    > > +asmlinkage int sys_revoke(const char __user *filename)
    > > +{
    > > + int err;
    > > + struct nameidata nd;
    > > +
    > > + err = __user_walk(filename, 0, &nd);
    > > + if (!err) {
    > > + err = do_revoke(nd.dentry->d_inode, NULL);
    > > + path_release(&nd);
    > > + }
    > > + return err;
    > > +}
    > > +
    > > +asmlinkage int sys_frevoke(unsigned int fd)
    > > +{
    > > + struct file *file = fget(fd);
    > > + int err = -EBADF;
    > > +
    > > + if (file) {
    > > + err = do_revoke(file->f_dentry->d_inode, file);
    > > + fput(file);
    > > + }
    > > + return err;
    > > +}
    >
    > Is that requiring only that user is able to refer file ?
    >
    >
    > BSD manual page for revoke(2) seems say:
    >
    > Access to a file may be revoked only by its owner or the super user.

    In do_revoke() there is:

    + if (current->fsuid != inode->i_uid && !capable(CAP_FOWNER)) {
    + ret = -EPERM;
    + goto out;

    That pretty much matches what the BSD manpage says.

    Björn
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