On Fri, Apr 22, 2016 at 8:14 AM, Philipp Gesang <phg@phi-gamma.net> wrote:

···<date: 2016-04-22, Friday>···<from: luigi scarso>···

> On Thu, Apr 21, 2016 at 10:20 PM, Philipp Gesang <phg@phi-gamma.net> wrote:
>
> > When passed the empty string, tprint() will allocate a zero-length
> > buffer and then branch on its first element (``if (*buffer) { … }``)
> > which has never been initialized.
> >
> > Prevent the invalid access by checking for the empty string and skipping
> > the printing routine entirely if appropriate.
> >
> > Signed-off-by: Philipp Gesang <phg@phi-gamma.net>
> > ---
> >  source/texk/web2c/luatexdir/tex/printing.w | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/source/texk/web2c/luatexdir/tex/printing.w
> > b/source/texk/web2c/luatexdir/tex/printing.w
> > index 478d55f..675fa45 100644
> > --- a/source/texk/web2c/luatexdir/tex/printing.w
> > +++ b/source/texk/web2c/luatexdir/tex/printing.w
> > @@ -367,6 +367,10 @@ void tprint(const char *sss)
> >      int newlinechar = int_par(new_line_char_code);
> >      int dolog = 0;
> >      int doterm = 0;
> > +    const size_t sss_len = strlen(sss);
> > +    if (sss_len == 0u) { /* nothing to print */
> > +        return;
> > +    }
> >      switch (selector) {
> >          case no_print:
> >              return;
> > @@ -413,7 +417,7 @@ void tprint(const char *sss)
> >      }
> >      /* what is left is the 3 term/log settings */
> >      if (dolog || doterm) {
> > -        buffer = xmalloc(strlen(sss)*3);
> > +        buffer = xmalloc(sss_len*3);
> >          if (dolog) {
> >              const unsigned char *ss = (const unsigned char *) sss;
> >              while (*ss) {
> > --
> > 2.8.0
> >
> >
> do you have an example that trigger the wrong sss string ?

For one it happens if the function is called on the empty string.
Here’s a test file:

    a\bye

I use revision 5949. With the Plain loader from the pretest I
get:

    $ valgrind --trace-children=yes mtxrun --script plain tprint-empty.tex
    …
    ==3758== Conditional jump or move depends on uninitialised value(s)
    ==3758==    at 0x4D77BE: tprint (printing.w:431)
    ==3758==    by 0x4D7A69: tprint_nl (printing.w:471)
    ==3758==    by 0x4BC19F: write_out (extensions.w:533)
    ==3758==    by 0x5B6BA4: out_what (pdflistout.w:262)
    ==3758==    by 0x4BBBAF: do_extension (extensions.w:389)
    ==3758==    by 0x4BBDF0: do_extension (extensions.w:418)
    ==3758==    by 0x4C2298: run_extension (maincontrol.w:616)
    ==3758==    by 0x4C43C2: main_control (maincontrol.w:971)
    ==3758==    by 0x4C0BAB: main_body (mainbody.w:461)
    ==3758==    by 0x4892B5: main (luatex.c:498)

Actually I just noticed that my patch is probably incorrect:
writeout invokes tprint_nl that way for the side effect of
popping a newline. The fix should thus be added further down
after that happened.

ok, thank you for the report.

--

luigi