main/screen: use better patch for CVE-2021-26937

The patch from Debian will result in screen stop propertly processing
combining characters after all slots have been exhausted.

main/screen/APKBUILD

@@ -2,7 +2,7 @@
 # Maintainer: Natanael Copa <ncopa@alpinelinux.org>
 pkgname=screen
 pkgver=4.8.0
-pkgrel=4
+pkgrel=5
 pkgdesc="Window manager that multiplexes a physical terminal"
 url="https://www.gnu.org/software/screen/"
 arch="all"
@@ -50,4 +50,4 @@ package() {
 
 sha512sums="770ebaf6ee9be711bcb8a6104b3294f2bf4523dae6683fdc5eac4b3aff7e511be2d922b6b2ad28ec241113c2e4fe0d80f9a482ae1658adc19c8c3a3680caa25c  screen-4.8.0.tar.gz
 82aca3e16c8cd7a3029d3b589ff2dd3471708d6287979ebb5cfdaedbd1f3012c0cd660b131e0cbe142b99786e49ef8b24c63159523d870e95ccf71ec94b82634  utmpx.patch
-1c9fec7b971d1674c8be9b0b540d33bb977d63b1bffe3d38fb0d23a75dd5137eac482b9388f4a0affe15717a7814c3913f0c2290876e50ac20bc5cff82c0606d  CVE-2021-26937.patch"
+21f296fa558ef5cdde378fcd8d47cf780f99702c3f798387f611260f29700397591f1757d1d3197a12650a4042af74176753e69bc19997c2bbfbb02b413a50a5  CVE-2021-26937.patch"

main/screen/CVE-2021-26937.patch

-Description: [CVE-2021-26937] Fix out of bounds array access
-Author: Axel Beckert <abe@debian.org>
-Bug-Debian: https://bugs.debian.org/982435
-Bug: https://savannah.gnu.org/bugs/?60030
-Bug: https://lists.gnu.org/archive/html/screen-devel/2021-02/msg00000.html
-Bug-OSS-Security: https://www.openwall.com/lists/oss-security/2021/02/09/3
-Forwarded: https://lists.gnu.org/archive/html/screen-devel/2021-02/msg00004.html
-
+Source: https://lists.gnu.org/archive/html/screen-devel/2021-02/msg00010.html
+diff --git a/encoding.c b/encoding.c
+index e5db3e7..79f5d14 100644
 --- a/encoding.c
 +++ b/encoding.c
-@@ -1408,21 +1408,23 @@
- 	}
-       /* FIXME: delete old char from all buffers */
-     }
--  else if (!combchars[i])
--    {
--      combchars[i] = (struct combchar *)malloc(sizeof(struct combchar));
--      if (!combchars[i])
--	return;
--      combchars[i]->prev = i;
--      combchars[i]->next = i;
--    }
--  combchars[i]->c1 = c1;
--  combchars[i]->c2 = c;
--  mc->image = i & 0xff;
--  mc->font  = (i >> 8) + 0xd8;
--  mc->fontx = 0;
--  debug3("combinig char %x %x -> %x\n", c1, c, i + 0xd800);
+@@ -43,7 +43,7 @@ static int  encmatch __P((char *, char *));
+ # 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 @@ int c;
+     {0x30000, 0x3FFFD},
+   };
+ 
++  if (c >= 0xdf00 && c <= 0xdfff)
++    return 1;          /* dw combining sequence */
+   return ((bisearch(c, wide, sizeof(wide) / sizeof(struct interval) - 1)) ||
+           (cjkwidth &&
+            bisearch(c, ambiguous,
+@@ -1330,11 +1332,12 @@ int c;
+ }
+ 
+ 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 @@ struct mchar *mc;
+     {
+       /* 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 @@ struct mchar *mc;
+   mc->font  = (i >> 8) + 0xd8;
+   mc->fontx = 0;
+   debug3("combinig char %x %x -> %x\n", c1, c, i + 0xd800);
 -  comb_tofront(root, i);
-+  else if (i < sizeof combchars / sizeof *combchars) {
-+    if (!combchars[i])
-+      {
-+        combchars[i] = (struct combchar *)malloc(sizeof(struct combchar));
-+        if (!combchars[i])
-+          return;
-+        combchars[i]->prev = i;
-+        combchars[i]->next = i;
-+      }
-+    combchars[i]->c1 = c1;
-+    combchars[i]->c2 = c;
-+    mc->image = i & 0xff;
-+    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 */