- bprm->buf[BINPRM_BUF_SIZE - 1] = '\0';
- if ((cp = strchr(bprm->buf, '\n')) == NULL)
- cp = bprm->buf+BINPRM_BUF_SIZE-1;
+ /*
+ * This section handles parsing the #! line into separate
+ * interpreter path and argument strings. We must be careful
+ * because bprm->buf is not yet guaranteed to be NUL-terminated
+ * (though the buffer will have trailing NUL padding when the
+ * file size was smaller than the buffer size).
+ *
+ * We do not want to exec a truncated interpreter path, so either
+ * we find a newline (which indicates nothing is truncated), or
+ * we find a space/tab/NUL after the interpreter path (which
+ * itself may be preceded by spaces/tabs). Truncating the
+ * arguments is fine: the interpreter can re-read the script to
+ * parse them on its own.
+ */
+ buf_end = bprm->buf + sizeof(bprm->buf) - 1;
+ cp = strnchr(bprm->buf, sizeof(bprm->buf), '\n');
+ if (!cp) {
+ cp = next_non_spacetab(bprm->buf + 2, buf_end);
+ if (!cp)
+ return -ENOEXEC; /* Entire buf is spaces/tabs */
+ /*
+ * If there is no later space/tab/NUL we must assume the
+ * interpreter path is truncated.
+ */
+ if (!next_terminator(cp, buf_end))
+ return -ENOEXEC;
+ cp = buf_end;
+ }
+ /* NUL-terminate the buffer and any trailing spaces/tabs. */