Fix CVE-2021-26937 for real: segfaults by displaying some UTF-8 characters

This is a recommit of r565281 fixing a typo in r565281, causing
a regression.

CVE-2021-26937 segfaults when displayingsome UTF-8 characters
described in
https://lists.gnu.org/archive/html/screen-devel/2021-02/msg00000.html.

PR:		253515
Reported by:	daniel.engberg.lists at pyret.net
Obtained from:	https://build.opensuse.org/request/show/871482
MFH:		2020Q1
Security:	CVE-2021-26937

3 files changed, 81 insertions, 1 deletions

diff --git a/sysutils/screen/Makefile b/sysutils/screen/Makefile
index 4c4f93966e97..f93f5bde2e00 100644
--- a/sysutils/screen/Makefile
+++ b/sysutils/screen/Makefile
@@ -3,7 +3,7 @@
 
 PORTNAME=	screen
 PORTVERSION=	4.8.0
-PORTREVISION=	2
+PORTREVISION=	3
 CATEGORIES=	sysutils
 MASTER_SITES=	GNU \
 		ftp://ftp.gnu.org/gnu/screen/ \
diff --git a/sysutils/screen/files/patch-ansi.c b/sysutils/screen/files/patch-ansi.c
new file mode 100644
index 000000000000..74ed96c079cd
--- /dev/null
+++ b/sysutils/screen/files/patch-ansi.c
@@ -0,0 +1,24 @@
+--- ansi.c.orig	2020-02-05 12:09:38.000000000 -0800
++++ ansi.c	2021-02-14 11:10:31.759160000 -0800
+@@ -692,10 +692,6 @@
+ 		    }
+ 		  curr->w_rend.font = 0;
+ 		}
+-#  ifdef DW_CHARS
+-	      if (curr->w_encoding == UTF8 && utf8_isdouble(c))
+-		curr->w_mbcs = 0xff;
+-#  endif
+ 	      if (curr->w_encoding == UTF8 && c >= 0x0300 && utf8_iscomb(c))
+ 		{
+ 		  int ox, oy;
+@@ -730,6 +726,10 @@
+ 		    }
+ 		  break;
+ 		}
++#  ifdef DW_CHARS
++	      if (curr->w_encoding == UTF8 && utf8_isdouble(c))
++		curr->w_mbcs = 0xff;
++#  endif
+ 	      font = curr->w_rend.font;
+ # endif
+ # ifdef DW_CHARS
diff --git a/sysutils/screen/files/patch-encoding.c b/sysutils/screen/files/patch-encoding.c
new file mode 100644
index 000000000000..0702f6b0a05c
--- /dev/null
+++ b/sysutils/screen/files/patch-encoding.c
@@ -0,0 +1,56 @@
+--- encoding.c.orig	2020-02-05 12:09:38.000000000 -0800
++++ encoding.c	2021-02-14 11:15:26.074193000 -0800
+@@ -43,7 +43,7 @@
+ # ifdef UTF8
+ static int   recode_char __P((int, int, int));
+ static int   recode_char_to_encoding __P((int, int));
+-static void  comb_tofront __P((int, int));
++static void  comb_tofront __P((int));
+ #  ifdef DW_CHARS
+ static int   recode_char_dw __P((int, int *, int, int));
+ static int   recode_char_dw_to_encoding __P((int, int *, int));
+@@ -1263,6 +1263,8 @@
+     {0x30000, 0x3FFFD},
+   };
+ 
++  if (c >= 0xdf00 && c <= 0xdfff)
++	return 1;	/* dw comining sequence */
+   return ((bisearch(c, wide, sizeof(wide) / sizeof(struct interval) - 1)) ||
+           (cjkwidth &&
+            bisearch(c, ambiguous,
+@@ -1330,11 +1332,12 @@
+ }
+ 
+ static void
+-comb_tofront(root, i)
+-int root, i;
++comb_tofront( i)
++int i;
+ {
+   for (;;)
+     {
++      int root = i >= 0x700 ? 0x801 : 0x800;
+       debug1("bring to front: %x\n", i);
+       combchars[combchars[i]->prev]->next = combchars[i]->next;
+       combchars[combchars[i]->next]->prev = combchars[i]->prev;
+@@ -1396,9 +1399,9 @@
+     {
+       /* full, recycle old entry */
+       if (c1 >= 0xd800 && c1 < 0xe000)
+-        comb_tofront(root, c1 - 0xd800);
++        comb_tofront(c1 - 0xd800);
+       i = combchars[root]->prev;
+-      if (c1 == i + 0xd800)
++      if (i == 0x800 || i == 0x801 || c1 == i + 0xd800)
+ 	{
+ 	  /* completely full, can't recycle */
+ 	  debug("utf8_handle_comp: completely full!\n");
+@@ -1422,7 +1425,7 @@
+   mc->font  = (i >> 8) + 0xd8;
+   mc->fontx = 0;
+   debug3("combinig char %x %x -> %x\n", c1, c, i + 0xd800);
+-  comb_tofront(root, i);
++  comb_tofront(i);
+ }
+ 
+ #else /* !UTF8 */