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[CVE-2026-4738] infback9: Remove offset pointer optimization in inftrees.c. #1235

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[CVE-2026-4738] infback9: Remove offset pointer optimization in inftrees.c. #1235

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18 changes: 8 additions & 10 deletions contrib/infback9/inftree9.c
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Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,7 @@ int inflate_table9(codetype type, unsigned short FAR *lens, unsigned codes,
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 */
Expand Down Expand Up @@ -170,19 +170,17 @@ int inflate_table9(codetype type, unsigned short FAR *lens, unsigned codes,
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 */
Expand All @@ -205,13 +203,13 @@ int inflate_table9(codetype type, unsigned short FAR *lens, unsigned codes,
for (;;) {
/* create table entry */
this.bits = (unsigned char)(len - drop);
if ((int)(work[sym]) < end) {
if ((unsigned)(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 */
Expand Down