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authorKarl Berry <karl@freefriends.org>2024-02-26 15:53:56 +0000
committerKarl Berry <karl@freefriends.org>2024-02-26 15:53:56 +0000
commit5c82c89e2aa8bf48118beea9f5367811b7b0efff (patch)
treeaf96612a8b04d35b922ef83310117b767f4a425e /Build/source/texk/web2c/unbalanced-braces.ch
parent2072014e12035985012120f58453b8e77fc85d5e (diff)
avoid crashing on devious uses of \output and write braces, from DRF (pdftex and xetex only)
git-svn-id: svn://tug.org/texlive/trunk@70173 c570f23f-e606-0410-a88d-b1316a301751
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+% $Id$
+% Fix overrun/underrun of \write and \output. David Fuchs, 2024.
+% Public domain.
+%
+% Changes for full defense against over-running (or under-running)
+% an \output or \write and ending up in all sorts of ill-defined
+% trouble. (Including the case of \output=\toks with no braces.)
+%
+% For some problematic input files, see tests/unbalanced-braces.test
+% (not a runnable test).
+%
+% The idea is that when it's time to run/evaluate each \output or \write,
+% they have to come to an end exactly as expected: at the right brace that
+% came from when they were first scanned to begin with; no amount of
+% monkey business with "funny braces" or \noexpand or \expandafter or \let
+% or whatever other trick you can think of should be able to get around
+% it. And you can't get away with going even one token past where you were
+% supposed to stop.
+%
+% To reiterate, fatal errors from this result in the terminal show just:
+% ! Emergency stop.
+% with no details on what/why. You have to look in the .log file for
+% the (terse) specifics:
+% Unbalanced output routine
+%
+% It's rather draconian, calling fatal_error when there's a problem,
+% but users really have no business trying to get anywhere near this
+% sort of thing on purpose. I sure hope nobody has found any use for
+% such undefined behaviors.
+
+% The changes assume locnull-optimize.ch has been applied. Unfortunately
+% the semantically-related changes have to be broken up to apply in
+% tex.web order.
+
+% emacs-page
+%% Catch extra left braces in \output right when finished scanning it.
+%
+@x [23.324] l.7000 p.B139
+ if token_type=macro then {parameters must be flushed}
+ while param_ptr>param_start do
+ begin decr(param_ptr);
+ flush_list(param_stack[param_ptr]);
+ end;
+@y
+ if token_type=macro then {parameters must be flushed}
+ while param_ptr>param_start do
+ begin decr(param_ptr);
+ flush_list(param_stack[param_ptr]);
+ end
+ else if (token_type=output_text)and(output_active) then
+ fatal_error("Unbalanced output routine");
+@.Unbalanced output routine@>
+@z
+
+%% Catch extra right braces in the \output routine.
+% <Resume the page builder...> tried, but needs to be more robust against
+% a backed-up right (funny) brace in the middle of \output masquerading
+% as the end-of-\output right brace.
+%
+% Reorder these so that end_token_list sees output_active=false.
+% 1) In back_input:
+@x [23.325] l.7025 p.B139
+begin while (loc=null)and(token_type<>v_template) do
+ end_token_list; {conserve stack space}
+@y
+begin while (loc=null)and(token_type<>v_template)
+ and(token_type<>output_text) do
+ end_token_list; {conserve stack space}
+@z
+
+%% Catch extra left braces finishing scanning a \write_text.
+%
+% In <Input from token list...> don't allow end_write while we're
+% still scanning through the write_text.
+@x [24.357] l.7488 p.B150
+ else check_outer_validity;
+@y
+ else
+ begin
+ if (cur_cs=end_write)and(mode=0) then
+ fatal_error("Unbalanced write command");
+ check_outer_validity;
+ end;
+@z
+
+%% Returning to catching extra right braces.
+%
+% 2) In <Feed the macro body and its parameters to the scanner>:
+@x [25.390] l.7983 p.B161
+while (loc=null)and(token_type<>v_template) do
+ end_token_list; {conserve stack space}
+@y
+while (loc=null)and(token_type<>v_template)
+ and(token_type<>output_text) do
+ end_token_list; {conserve stack space}
+@z
+
+% We know we've just scanned a right brace that seems to be the end
+% of the \output routine. But maybe it had been backed-up over,
+% and we've lost the output_text in the call to back_input. So,
+% the checking gets sloppy. But now we're sure to keep the
+% (finished) output_text level around, so we can always check
+% that we were just finished with it, so it's where the brace
+% came from.
+
+% In <Resume the page builder after an output routine has come to an end>:
+@x [45.1026] l.19938 p.B432
+begin if (loc<>null) or
+ ((token_type<>output_text)and(token_type<>backed_up)) then
+ @<Recover from an unbalanced output routine@>;
+@y
+begin
+ while (state=token_list)and(loc=null)and(token_type=backed_up) do
+ end_token_list; {output-ending brace may have been backed-up}
+ if (state<>token_list)or(loc<>null)or(token_type<>output_text) then
+ @<Recover from an unbalanced output routine@>;
+@z
+
+% In <Resume the page builder after an output routine has come to an end>:
+@x [45.1026] l.19941 p.B432
+end_token_list; {conserve stack space in case more outputs are triggered}
+end_graf; unsave; output_active:=false; insert_penalties:=0;@/
+@y
+end_graf; unsave; output_active:=false; insert_penalties:=0;@/
+end_token_list; {conserve stack space in case more outputs are triggered}
+@z
+
+% <Expand macros in the token list and...> had set mode:=0 while
+% expanding the \write token list.
+
+% Reorder these statements so that the final get_token that's supposed to
+% scan off the end_write_token will have mode<>0 if everything lined up:
+@x [53.1371] l.24884 p.B546
+get_token;@+if cur_tok<>end_write_token then
+ @<Recover from an unbalanced write command@>;
+mode:=old_mode;
+@y
+mode:=old_mode;
+get_token;@+if cur_tok<>end_write_token then
+ @<Recover from an unbalanced write command@>;
+@z