bug#59544: [PATCH] Fixed lib-src/etags.c command execute vulnerability

[Stefan Kangas]

"lux" <lx@shellcodes.org> writes:

> I rewrote this code, not use system(1).

Thanks.

> From d6bc71f8640efe7caa2657a75c5aa4d8b4f0532c Mon Sep 17 00:00:00 2001
> From: lu4nx <lx@shellcodes.org>
> Date: Fri, 25 Nov 2022 14:38:29 +0800
> Subject: [PATCH] * Fixed lib-src/etags.c command execute vulnerability
>
> ---
>  lib-src/etags.c | 44 +++++++++++++++++++++++++++++++-------------
>  1 file changed, 31 insertions(+), 13 deletions(-)
>
> diff --git a/lib-src/etags.c b/lib-src/etags.c
> index f665f35fa6..1bb352f565 100644
> --- a/lib-src/etags.c
> +++ b/lib-src/etags.c
> @@ -1387,9 +1387,11 @@ main (int argc, char **argv)
>    /* From here on, we are in (CTAGS && !cxref_style) */
>    if (update)
>      {
> -      char *cmd =
> -     xmalloc (strlen (tagfile) + whatlen_max +
> -              sizeof "mv..OTAGS;grep -Fv '\t\t' OTAGS >;rm OTAGS");
> +      FILE *otags_f, *tag_f;
> +      int buf_len;
> +      char *buf;
> +      char line[512];

Hmm, I'm not sure about the hard-coded 512 character line limit here.
ISTR that some people use much longer lines than that.

Could we do without it?

(As a matter of style, I would just declare the types at first use,
which limits their scope and makes the code easier to read.  But it's up
to you.)

> +
>        for (i = 0; i < current_arg; ++i)
>       {
>         switch (argbuffer[i].arg_type)
> @@ -1400,17 +1402,33 @@ main (int argc, char **argv)
>           default:
>             continue;         /* the for loop */
>           }
> -       char *z = stpcpy (cmd, "mv ");
> -       z = stpcpy (z, tagfile);
> -       z = stpcpy (z, " OTAGS;grep -Fv '\t");
> -       z = stpcpy (z, argbuffer[i].what);
> -       z = stpcpy (z, "\t' OTAGS >");
> -       z = stpcpy (z, tagfile);
> -       strcpy (z, ";rm OTAGS");
> -       if (system (cmd) != EXIT_SUCCESS)
> -         fatal ("failed to execute shell command");
> +
> +          otags_f = fopen ("OTAGS", "w");
> +          tag_f = fopen (tagfile, "r");
> +
> +          if (otags_f == NULL)
> +            pfatal ("OTAGS");
> +
> +          if (tag_f == NULL)
> +            pfatal (tagfile);
> +
> +          buf_len = strlen (argbuffer[i].what) + sizeof ("\t\t ") + 1;
> +          buf = xmalloc (buf_len);
> +          snprintf (buf, buf_len, "\t%s\t", argbuffer[i].what);
> +
> +          while (fgets (line, sizeof (line), tag_f) != NULL)

We should check ferror(tag_f), too and croak if there is a problem.

> +            {
> +              if (strstr (line, buf) == NULL)
> +                fputs (line, otags_f);

Missing error handling for fputs.

> +            }
> +
> +          fclose (otags_f);
> +          fclose (tag_f);

Should be:

if (fclose (otags_f) == EOF)
    pfatal (otags_f);
if (fclose (tag_f) == EOF)
    pfatal (tag_f);

> +
> +          rename ("OTAGS", tagfile);
> +          unlink ("OTAGS");

Please add error handling for both of these.

>       }
> -      free (cmd);
> +

Nit: I don't think the empty line helps here?

>        append_to_tagfile = true;
>      }