backup: prevent a symlink attack by operating on the file descriptor
Use futimens() instead of utime() to change the timestamps on a backup file. Otherwise, a non-privileged user could create an arbitrary symlink with the name of the backup file and in this way fool a privileged user to call utime() on the attacker-chosen file. Import the relevant gnulib module to make sure futimens() is available.
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@ -5,6 +5,7 @@ gnulib_url="git://git.sv.gnu.org/gnulib.git"
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gnulib_hash="4084b3a1094372b960ce4a97634e08f4538c8bdd"
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modules="
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futimens
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getdelim
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getline
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getopt-gnu
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24
src/files.c
24
src/files.c
@ -1541,12 +1541,14 @@ void init_backup_dir(void)
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/* Read from inn, write to out. We assume inn is opened for reading,
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* and out for writing. We return 0 on success, -1 on read error, or -2
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* on write error. */
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int copy_file(FILE *inn, FILE *out)
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* on write error. inn is always closed by this function, out is closed
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* only if close_out is true. */
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int copy_file(FILE *inn, FILE *out, bool close_out)
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{
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int retval = 0;
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char buf[BUFSIZ];
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size_t charsread;
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int (*flush_out_fnc)(FILE *) = (close_out) ? fclose : fflush;
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assert(inn != NULL && out != NULL && inn != out);
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@ -1564,7 +1566,7 @@ int copy_file(FILE *inn, FILE *out)
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if (fclose(inn) == EOF)
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retval = -1;
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if (fclose(out) == EOF)
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if (flush_out_fnc(out) == EOF)
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retval = -2;
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return retval;
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@ -1655,13 +1657,13 @@ bool write_file(const char *name, FILE *f_open, bool tmp,
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int backup_fd;
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FILE *backup_file;
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char *backupname;
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struct utimbuf filetime;
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static struct timespec filetime[2];
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int copy_status;
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int backup_cflags;
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/* Save the original file's access and modification times. */
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filetime.actime = openfile->current_stat->st_atime;
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filetime.modtime = openfile->current_stat->st_mtime;
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filetime[0].tv_sec = openfile->current_stat->st_atime;
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filetime[1].tv_sec = openfile->current_stat->st_mtime;
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if (f_open == NULL) {
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/* Open the original file to copy to the backup. */
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@ -1790,7 +1792,7 @@ bool write_file(const char *name, FILE *f_open, bool tmp,
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#endif
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/* Copy the file. */
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copy_status = copy_file(f, backup_file);
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copy_status = copy_file(f, backup_file, FALSE);
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if (copy_status != 0) {
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statusline(ALERT, _("Error reading %s: %s"), realname,
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@ -1799,7 +1801,8 @@ bool write_file(const char *name, FILE *f_open, bool tmp,
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}
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/* And set its metadata. */
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if (utime(backupname, &filetime) == -1 && !ISSET(INSECURE_BACKUP)) {
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if (futimens(backup_fd, filetime) == -1 && !ISSET(INSECURE_BACKUP)) {
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fclose(backup_file);
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if (prompt_failed_backupwrite(backupname))
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goto skip_backup;
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statusline(HUSH, _("Error writing backup file %s: %s"),
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@ -1811,6 +1814,7 @@ bool write_file(const char *name, FILE *f_open, bool tmp,
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goto cleanup_and_exit;
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}
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fclose(backup_file);
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free(backupname);
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}
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@ -1867,7 +1871,7 @@ bool write_file(const char *name, FILE *f_open, bool tmp,
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}
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}
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if (f_source == NULL || copy_file(f_source, f) != 0) {
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if (f_source == NULL || copy_file(f_source, f, TRUE) != 0) {
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statusline(ALERT, _("Error writing temp file: %s"),
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strerror(errno));
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unlink(tempname);
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@ -1975,7 +1979,7 @@ bool write_file(const char *name, FILE *f_open, bool tmp,
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goto cleanup_and_exit;
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}
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if (copy_file(f_source, f) == -1) {
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if (copy_file(f_source, f, TRUE) == -1) {
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statusline(ALERT, _("Error writing %s: %s"), realname,
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strerror(errno));
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goto cleanup_and_exit;
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@ -298,7 +298,7 @@ void init_backup_dir(void);
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int delete_lockfile(const char *lockfilename);
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int write_lockfile(const char *lockfilename, const char *origfilename, bool modified);
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#endif
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int copy_file(FILE *inn, FILE *out);
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int copy_file(FILE *inn, FILE *out, bool close_out);
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bool write_file(const char *name, FILE *f_open, bool tmp,
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kind_of_writing_type method, bool nonamechange);
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#ifndef NANO_TINY
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