improve fmt/base corruption checks, from DRF

git-svn-id: svn://tug.org/texlive/trunk@68900 c570f23f-e606-0410-a88d-b1316a301751

3 files changed, 24 insertions, 4 deletions

diff --git a/Build/source/texk/web2c/ChangeLog b/Build/source/texk/web2c/ChangeLog
index d8b8c81d16c..06b9647abec 100644
--- a/Build/source/texk/web2c/ChangeLog
+++ b/Build/source/texk/web2c/ChangeLog
@@ -1,3 +1,9 @@
+2023-11-19  Karl Berry  <karl@freefriends.org>
+
+	* tex.ch,
+	* mf.ch (Undump the dynamic memory): improve fmt/base corruption
+	tests, from DRF.
+
 2023-11-19  Andreas Scherer  <https://ascherer.github.io>
 
 	* ctangleboot.cin,
diff --git a/Build/source/texk/web2c/mf.ch b/Build/source/texk/web2c/mf.ch
index 4b13cacb441..af7a1ca1e9f 100644
--- a/Build/source/texk/web2c/mf.ch
+++ b/Build/source/texk/web2c/mf.ch
@@ -1854,12 +1854,19 @@ mem:=xmalloc_array (memory_word, mem_max - mem_min + 1);
 @z
 
 @x [48.1195] l.22714 - Check that p did not become corrupt.
+p:=q+node_size(q);
 if (p>lo_mem_max)or((q>=rlink(q))and(rlink(q)<>rover)) then goto off_base;
 @y
 {If the base file is messed up, that addition to |p| might cause it to
  become garbage. Report from Gregory James DUCK to Karl, 14 Sep 2023.
- Found with a fuzz tester similar to AFL-fuzz. Also changed in \TeX.}
-if (p<mem_min)or(p>lo_mem_max)or((q>=rlink(q))and(rlink(q)<>rover)) then goto off_base;
+ Also changed in \MF. Fix from DRF, who explains: we test before doing the
+ addition to avoid assuming silent wrap-around overflow, and also to to
+ catch cases where |node_size| was, say, bogusly the equivalent of $-1$
+ and thus |p+node_size| would still look valid.}
+if (node_size(q)>lo_mem_max-q) or (rlink(q)>lo_mem_max)
+   or ((q>=rlink(q))and(rlink(q)<>rover))
+then goto off_base;
+p:=q+node_size(q);
 @z
 
 @x [48.1199] l.22750 - Allow command line to override dumped value.
diff --git a/Build/source/texk/web2c/tex.ch b/Build/source/texk/web2c/tex.ch
index 51307bf7c7b..3243105730a 100644
--- a/Build/source/texk/web2c/tex.ch
+++ b/Build/source/texk/web2c/tex.ch
@@ -3654,12 +3654,19 @@ repeat undump_things(mem[p], q+2-p);
 @z
 
 @x [50.1312] l.23955 - Check that p did not become corrupt.
+p:=q+node_size(q);
 if (p>lo_mem_max)or((q>=rlink(q))and(rlink(q)<>rover)) then goto bad_fmt;
 @y
 {If the format file is messed up, that addition to |p| might cause it to
  become garbage. Report from Gregory James DUCK to Karl, 14 Sep 2023.
- Found with a fuzz tester similar to AFL-fuzz. Also changed in \MF.}
-if (p<mem_min)or(p>lo_mem_max)or((q>=rlink(q))and(rlink(q)<>rover)) then goto bad_fmt;
+ Also changed in \MF. Fix from DRF, who explains: we test before doing the
+ addition to avoid assuming silent wrap-around overflow, and also to to
+ catch cases where |node_size| was, say, bogusly the equivalent of $-1$
+ and thus |p+node_size| would still look valid.}
+if (node_size(q)>lo_mem_max-q) or (rlink(q)>lo_mem_max)
+   or ((q>=rlink(q))and(rlink(q)<>rover))
+then goto bad_fmt;
+p:=q+node_size(q);
 @z
 
 @x [50.1312] l.23878 - Make dumping/undumping more efficient.