Since the FreeBSD local modifications are mostly trivial (consisting

primarily of pointless $FreeBSD$ tags), sync most files in HEAD with
those in the ZLIB branch.  This minimizes the differences between
HEAD and ZLIB and should simplify future imports.

After this, there are only three files with local modifications
(gzio.c, minigzip.c, and zconf.h) and two non-vendor files
(Makefile, zopen.c).  The rest exactly match the vendor distribution.

PR:		i386/76294
MFC after:	2 weeks

1 files changed, 50 insertions, 29 deletions

diff --git a/lib/libz/crc32.c b/lib/libz/crc32.c
index efb152ac..b39c7e1 100644
--- a/lib/libz/crc32.c
+++ b/lib/libz/crc32.c
@@ -9,8 +9,15 @@
  * of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
  */
 
-#include <sys/cdefs.h>
-__FBSDID("$FreeBSD$");
+/* @(#) $Id$ */
+
+/*
+  Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
+  protection on the static variables used to control the first-use generation
+  of the crc tables.  Therefore, if you #define DYNAMIC_CRC_TABLE, you should
+  first call get_crc_table() to initialize the tables before allowing more than
+  one thread to use crc32().
+ */
 
 #ifdef MAKECRCH
 #  include <stdio.h>
@@ -59,7 +66,7 @@ __FBSDID("$FreeBSD$");
 
 #ifdef DYNAMIC_CRC_TABLE
 
-local int crc_table_empty = 1;
+local volatile int crc_table_empty = 1;
 local unsigned long FAR crc_table[TBLS][256];
 local void make_crc_table OF((void));
 #ifdef MAKECRCH
@@ -96,38 +103,51 @@ local void make_crc_table()
 {
     unsigned long c;
     int n, k;
-    unsigned long poly;            /* polynomial exclusive-or pattern */
+    unsigned long poly;                 /* polynomial exclusive-or pattern */
     /* terms of polynomial defining this crc (except x^32): */
+    static volatile int first = 1;      /* flag to limit concurrent making */
     static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
 
-    /* make exclusive-or pattern from polynomial (0xedb88320UL) */
-    poly = 0UL;
-    for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
-        poly |= 1UL << (31 - p[n]);
-
-    /* generate a crc for every 8-bit value */
-    for (n = 0; n < 256; n++) {
-        c = (unsigned long)n;
-        for (k = 0; k < 8; k++)
-            c = c & 1 ? poly ^ (c >> 1) : c >> 1;
-        crc_table[0][n] = c;
-    }
+    /* See if another task is already doing this (not thread-safe, but better
+       than nothing -- significantly reduces duration of vulnerability in
+       case the advice about DYNAMIC_CRC_TABLE is ignored) */
+    if (first) {
+        first = 0;
+
+        /* make exclusive-or pattern from polynomial (0xedb88320UL) */
+        poly = 0UL;
+        for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
+            poly |= 1UL << (31 - p[n]);
+
+        /* generate a crc for every 8-bit value */
+        for (n = 0; n < 256; n++) {
+            c = (unsigned long)n;
+            for (k = 0; k < 8; k++)
+                c = c & 1 ? poly ^ (c >> 1) : c >> 1;
+            crc_table[0][n] = c;
+        }
 
 #ifdef BYFOUR
-    /* generate crc for each value followed by one, two, and three zeros, and
-       then the byte reversal of those as well as the first table */
-    for (n = 0; n < 256; n++) {
-        c = crc_table[0][n];
-        crc_table[4][n] = REV(c);
-        for (k = 1; k < 4; k++) {
-            c = crc_table[0][c & 0xff] ^ (c >> 8);
-            crc_table[k][n] = c;
-            crc_table[k + 4][n] = REV(c);
+        /* generate crc for each value followed by one, two, and three zeros,
+           and then the byte reversal of those as well as the first table */
+        for (n = 0; n < 256; n++) {
+            c = crc_table[0][n];
+            crc_table[4][n] = REV(c);
+            for (k = 1; k < 4; k++) {
+                c = crc_table[0][c & 0xff] ^ (c >> 8);
+                crc_table[k][n] = c;
+                crc_table[k + 4][n] = REV(c);
+            }
         }
-    }
 #endif /* BYFOUR */
 
-  crc_table_empty = 0;
+        crc_table_empty = 0;
+    }
+    else {      /* not first */
+        /* wait for the other guy to finish (not efficient, but rare) */
+        while (crc_table_empty)
+            ;
+    }
 
 #ifdef MAKECRCH
     /* write out CRC tables to crc32.h */
@@ -181,9 +201,10 @@ local void write_table(out, table)
 const unsigned long FAR * ZEXPORT get_crc_table()
 {
 #ifdef DYNAMIC_CRC_TABLE
-  if (crc_table_empty) make_crc_table();
+    if (crc_table_empty)
+        make_crc_table();
 #endif /* DYNAMIC_CRC_TABLE */
-  return (const unsigned long FAR *)crc_table;
+    return (const unsigned long FAR *)crc_table;
 }
 
 /* ========================================================================= */