From: Simone Piccardi Date: Sun, 21 Apr 2019 16:07:41 +0000 (+0200) Subject: Test per linkat X-Git-Url: https://gapil.gnulinux.it/gitweb/?a=commitdiff_plain;h=be93b54a4875d772cce5cbff77d32241039d0367;p=gapil.git Test per linkat --- diff --git a/fileio.tex b/fileio.tex index b1b78b4..94ac81d 100644 --- a/fileio.tex +++ b/fileio.tex @@ -2197,18 +2197,17 @@ l'argomento \param{flags},\footnote{nei kernel precendenti, dall'introduzione valido, e doveva essere passato sempre con valore nullo.} che richiede di dereferenziare i collegamenti simbolici. Inoltre a partire dal kernel 3.11 si può usare \const{AT\_EMPTY\_PATH} per creare un nuovo \textit{hard link} al -file associato al file descriptor \param{olddirfd} (ottenuto ad esempio usando -\func{open} con \const{O\_PATH}) che però in questo caso non può essere una -directory. +file associato al file descriptor \param{olddirfd}. + % NOTE per la discussione sui problemi di sicurezza relativi a questa % funzionalità vedi http://lwn.net/Articles/562488/ -La funzione però prevede un comportamento specifico nel caso che +La funzione prevede inoltre un comportamento specifico nel caso che \param{olddirfd} faccia riferimento ad un file anonimo ottenuto usando \func{open} con \const{O\_TMPFILE}. In generale quando il file associato ad -\param{olddirfd} ha un numero di link nullo, la funzione fallisce, c'è però -una +\param{olddirfd} ha un numero di link nullo (come in questo caso), la funzione +fallisce, c'è però una l'uso di \const{AT\_EMPTY\_PATH} assume un significato diff --git a/sources/test_linkat.c b/sources/test_linkat.c new file mode 100644 index 0000000..b43fa23 --- /dev/null +++ b/sources/test_linkat.c @@ -0,0 +1,152 @@ +/* test_linkat.c + * + * Copyright (C) 2019 Simone Piccardi + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or (at + * your option) any later version. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + */ +/**************************************************************** + * + * Program test_linkat.c: + * Program to test use of linkat and O_TMPFILE and other combinations + * + * Author: Simone Piccardi + * Oct. 2018 + * + * Usage: testlinkat -h give all info's + * + ****************************************************************/ +/* + * Include needed headers + */ +#define _GNU_SOURCE +#include /* error definitions and routines */ +#include /* C standard library */ +#include /* unix standard library */ +#include /* standard I/O library */ +#include /* C strings library */ +#include +#include /* needed for dirname e basename */ +#include +#include +#include + +/* Help printing routine */ +void usage(void); + +int main(int argc, char *argv[]) +{ +/* + * Variables definition + */ + int i; + int wait=0; + char *srcfile = NULL; + /* + * Input section: decode command line parameters + * Use getopt function + */ + opterr = 0; /* don't want writing to stderr */ + while ( (i = getopt(argc, argv, "hw:f:")) != -1) { + switch (i) { + /* + * Handling options + */ + case 'h': /* help option */ + printf("Wrong -h option use\n"); + usage(); + return -1; + break; + case 'w': /* time to wait in s */ + wait = strtol(optarg, NULL, 10); /* convert input */ + break; + case 'f': /* using a source file */ + srcfile = optarg; + break; + case '?': /* unrecognized options */ + printf("Unrecognized options -%c\n",optopt); + usage(); + default: /* should not reached */ + usage(); + } + } + /* *********************************************************** + * + * Options processing completed + * + * Main code beginning + * + * ***********************************************************/ + /* There must be 1 remaing parameters */ + if ( (argc-optind) != 1 ) { + printf("From %d arguments, removed %d options\n", argc, optind); + usage(); + } + char *path, *dir, *file; + char pattern[] = "prova prova prova\n"; + path = strdup(argv[optind]); + file = basename(argv[optind]); + dir = dirname(argv[optind]); + printf("Working on dir %s file: %s\nwith path: %s\n", + dir, file, path); + int fd, newfd; + if ( ! srcfile ) { + fd = open(dir, O_TMPFILE|O_RDWR,S_IRUSR|S_IWUSR); + if ( fd <= 0 ) + perror("cannot open TMPFILE"); + if ( (i = write(fd, pattern, sizeof(pattern))) < 0 ) + perror("cannot write on TMPFILE"); + else + printf("saved %d chars on fd %d\n", i, fd); + } else { + printf("source is %s\n", srcfile); + if ( (fd = open(srcfile, O_RDONLY)) < 0 ) { + perror("cannot open source"); + exit(1); + } + } + newfd = open(dir, O_PATH|O_RDWR); + int err; + err = linkat(fd, "", newfd, file, AT_EMPTY_PATH); + if ( err < 0 ) { + perror("error on creating TMPFILE"); + printf("cannot link fd %d on fd %d, %s with AT_EMPTY_PATH\n", + fd, newfd, file); + char fdpath[PATH_MAX]; + snprintf(fdpath, PATH_MAX, "/proc/self/fd/%d", fd); + printf("fd path %s\n", fdpath); + err = linkat(AT_FDCWD, fdpath, newfd, file, AT_SYMLINK_FOLLOW); + if ( err < 0 ) { + perror("still error creating TMPFILE"); + sleep(wait); + exit(1); + } + if ( fchmodat(newfd, file,S_IRUSR|S_IWUSR,0) < 0 ) + perror("Cannot change permission to new file"); + } + free(path); + return 0; +} +/* + * routine to print usage info and exit + */ +void usage(void) { + printf("Program testlinkat : test fopen for a file \n"); + printf("Usage:\n"); + printf(" testfopen [-h] file mode \n"); + printf(" -h print this help\n"); + + exit(1); +} +