Nacked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
This is broken. If the referenced file is in a different mount namespace
the path returned could point to a completely different path in your
own mount namespace. Even in your own mount namespace this makes the
proc symlinks racy and not guaranteed to return the file of interest.
I don't see any hope of this approach ever working.
Eric
Jeff Layton <jlayton@xxxxxxxxxx> writes:
> -static int proc_pid_readlink(struct dentry * dentry, char __user * buffer, int buflen)
> -{
> - int error = -EACCES;
> - struct inode *inode = dentry->d_inode;
> + struct page *page = NULL;
> struct path path;
> + int error;
>
> /* Are we allowed to snoop on the tasks file descriptors? */
> - if (!proc_fd_access_allowed(inode))
> + if (!proc_fd_access_allowed(inode)) {
> + pathname = ERR_PTR(-EACCES);
> goto out;
> + }
>
> error = PROC_I(inode)->op.proc_get_link(inode, &path);
> - if (error)
> + if (error) {
> + pathname = ERR_PTR(error);
> goto out;
> + }
> +
> + page = alloc_page(GFP_HIGHUSER);
> + if (!page) {
> + pathname = ERR_PTR(-ENOMEM);
> + goto out_path_put;
> + }
> +
> + pathname = kmap(page);
> + pathname = d_path(&path, pathname, PAGE_SIZE);
This is just nonsense.
> + if (IS_ERR(pathname)) {
> + kunmap(page);
> + __free_page(page);
> + page = NULL;
> + }
>
> - error = do_proc_readlink(&path, buffer, buflen);
> +out_path_put:
> path_put(&path);
> out:
> - return error;
> + nd_set_link(nd, pathname);
> + return page;
> +}
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