From e9268e9c35c7cf5374ab3e64dc62005efa10b64c Mon Sep 17 00:00:00 2001
From: Su Yindu <yindusu@smu.edu.sg>
Date: Sun, 16 Feb 2025 23:35:47 +0800
Subject: [PATCH] Remove offset pointer optimization in inftrees.c. inftrees.c
 was subtracting an offset from a pointer to an array, in order to provide a
 pointer that allowed indexing starting at the offset. This is not compliant
 with the C standard, for which the behavior of a pointer decremented before
 its allocated memory is undefined. Per the recommendation of a security audit
 of the zlib code by Trail of Bits and TrustInSoft, in support of the Mozilla
 Foundation, this tiny optimization was removed, in order to avoid the
 possibility of undefined behavior.

---
 deps/zlib/contrib/infback9/inftree9.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/deps/zlib/contrib/infback9/inftree9.c b/deps/zlib/contrib/infback9/inftree9.c
index 5f4a76798..bd570e26f 100644
--- a/deps/zlib/contrib/infback9/inftree9.c
+++ b/deps/zlib/contrib/infback9/inftree9.c
@@ -54,7 +54,7 @@ unsigned short FAR *work;
     code FAR *next;             /* next available space in table */
     const unsigned short FAR *base;     /* base value table to use */
     const unsigned short FAR *extra;    /* extra bits table to use */
-    int end;                    /* use base and extra for symbol > end */
+    unsigned match;             /* use base and extra for symbol >= match */
     unsigned short count[MAXBITS+1];    /* number of codes of each length */
     unsigned short offs[MAXBITS+1];     /* offsets in table for each length */
     static const unsigned short lbase[31] = { /* Length codes 257..285 base */
@@ -175,19 +175,17 @@ unsigned short FAR *work;
     switch (type) {
     case CODES:
         base = extra = work;    /* dummy value--not used */
-        end = 19;
+        match = 20;
         break;
     case LENS:
         base = lbase;
-        base -= 257;
         extra = lext;
-        extra -= 257;
-        end = 256;
+        match = 257;
         break;
     default:            /* DISTS */
         base = dbase;
         extra = dext;
-        end = -1;
+        match = 0;
     }
 
     /* initialize state for loop */
@@ -210,13 +208,13 @@ unsigned short FAR *work;
     for (;;) {
         /* create table entry */
         this.bits = (unsigned char)(len - drop);
-        if ((int)(work[sym]) < end) {
+        if (work[sym] + 1 < match) {
             this.op = (unsigned char)0;
             this.val = work[sym];
         }
-        else if ((int)(work[sym]) > end) {
-            this.op = (unsigned char)(extra[work[sym]]);
-            this.val = base[work[sym]];
+        else if (work[sym] >= match) {
+            this.op = (unsigned char)(extra[work[sym] - match]);
+            this.val = base[work[sym] - match];
         }
         else {
             this.op = (unsigned char)(32 + 64);         /* end of block */