[Nasm-bugs] [Bug 3392513] New: NULL Pointer Dereference in asm/labels.c

[noreply-nasm at gorcunov.org]

https://bugzilla.nasm.us/show_bug.cgi?id=3392513

            Bug ID: 3392513
           Summary: NULL Pointer Dereference in asm/labels.c
           Product: NASM
           Version: unspecified
          Hardware: All
                OS: All
            Status: OPEN
          Severity: normal
          Priority: Medium
         Component: Assembler
          Assignee: nobody at nasm.us
          Reporter: mohdfakhrizulkifli at gmail.com
                CC: gorcunov at gmail.com, hpa at zytor.com, nasm-bugs at nasm.us
     Obtained from: Build from source archive using configure

Created attachment 411667
  --> https://bugzilla.nasm.us/attachment.cgi?id=411667&action=edit
crash poc

insn_is_label remains FALSE and therefore leaving result->label assigned to
NULL which is then dereference in islocal().

   [...]

    if (i == TOKEN_ID || (insn_is_label && i == TOKEN_INSN)) {    <-- not taken
        /* there's a label here */
        first = false;
        result->label = tokval.t_charptr;
        i = stdscan(NULL, &tokval);
        if (i == ':') {         /* skip over the optional colon */
            i = stdscan(NULL, &tokval);
        } else if (i == 0) {
            nasm_error(ERR_WARNING | ERR_WARN_OL | ERR_PASS1,
                  "label alone on a line without a colon might be in error");
        }
        if (i != TOKEN_INSN || tokval.t_integer != I_EQU) {
            /*
             * FIXME: location.segment could be NO_SEG, in which case
             * it is possible we should be passing 'absolute.segment'. Look
into this.
             * Work out whether that is *really* what we should be doing.
             * Generally fix things. I think this is right as it is, but
             * am still not certain.
             */
            define_label(result->label,
                         in_absolute ? absolute.segment : location.segment,
                         location.offset, true);
    [...]

static bool islocal(const char *l)
{
    if (tasm_compatible_mode) {
        if (l[0] == '@' && l[1] == '@')
            return true;
    }
    return (l[0] == '.' && l[1] != '.');  <-- boom
}

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