Skip to content
Permalink
Browse files

Use post-increment only in inffast.c.

An old inffast.c optimization turns out to not be optimal anymore
with modern compilers, and furthermore was not compliant with the
C standard, for which decrementing a pointer 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 "optimization" was removed, in order to
avoid the possibility of undefined behavior.
  • Loading branch information...
madler committed Sep 22, 2016
1 parent 3fb251b commit 9aaec95e82117c1cb0f9624264c3618fc380cecb
Showing with 31 additions and 50 deletions.
  1. +31 −50 inffast.c
@@ -10,25 +10,6 @@

#ifndef ASMINF

/* Allow machine dependent optimization for post-increment or pre-increment.
Based on testing to date,
Pre-increment preferred for:
- PowerPC G3 (Adler)
- MIPS R5000 (Randers-Pehrson)
Post-increment preferred for:
- none
No measurable difference:
- Pentium III (Anderson)
- M68060 (Nikl)
*/
#ifdef POSTINC
# define OFF 0
# define PUP(a) *(a)++
#else
# define OFF 1
# define PUP(a) *++(a)
#endif

/*
Decode literal, length, and distance codes and write out the resulting
literal and match bytes until either not enough input or output is
@@ -96,9 +77,9 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */

/* copy state to local variables */
state = (struct inflate_state FAR *)strm->state;
in = strm->next_in - OFF;
in = strm->next_in;
last = in + (strm->avail_in - 5);
out = strm->next_out - OFF;
out = strm->next_out;
beg = out - (start - strm->avail_out);
end = out + (strm->avail_out - 257);
#ifdef INFLATE_STRICT
@@ -119,9 +100,9 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
input data or output space */
do {
if (bits < 15) {
hold += (unsigned long)(PUP(in)) << bits;
hold += (unsigned long)(*in++) << bits;
bits += 8;
hold += (unsigned long)(PUP(in)) << bits;
hold += (unsigned long)(*in++) << bits;
bits += 8;
}
here = lcode[hold & lmask];
@@ -134,14 +115,14 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ?
"inflate: literal '%c'\n" :
"inflate: literal 0x%02x\n", here.val));
PUP(out) = (unsigned char)(here.val);
*out++ = (unsigned char)(here.val);
}
else if (op & 16) { /* length base */
len = (unsigned)(here.val);
op &= 15; /* number of extra bits */
if (op) {
if (bits < op) {
hold += (unsigned long)(PUP(in)) << bits;
hold += (unsigned long)(*in++) << bits;
bits += 8;
}
len += (unsigned)hold & ((1U << op) - 1);
@@ -150,9 +131,9 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
}
Tracevv((stderr, "inflate: length %u\n", len));
if (bits < 15) {
hold += (unsigned long)(PUP(in)) << bits;
hold += (unsigned long)(*in++) << bits;
bits += 8;
hold += (unsigned long)(PUP(in)) << bits;
hold += (unsigned long)(*in++) << bits;
bits += 8;
}
here = dcode[hold & dmask];
@@ -165,10 +146,10 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
dist = (unsigned)(here.val);
op &= 15; /* number of extra bits */
if (bits < op) {
hold += (unsigned long)(PUP(in)) << bits;
hold += (unsigned long)(*in++) << bits;
bits += 8;
if (bits < op) {
hold += (unsigned long)(PUP(in)) << bits;
hold += (unsigned long)(*in++) << bits;
bits += 8;
}
}
@@ -196,30 +177,30 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
if (len <= op - whave) {
do {
PUP(out) = 0;
*out++ = 0;
} while (--len);
continue;
}
len -= op - whave;
do {
PUP(out) = 0;
*out++ = 0;
} while (--op > whave);
if (op == 0) {
from = out - dist;
do {
PUP(out) = PUP(from);
*out++ = *from++;
} while (--len);
continue;
}
#endif
}
from = window - OFF;
from = window;
if (wnext == 0) { /* very common case */
from += wsize - op;
if (op < len) { /* some from window */
len -= op;
do {
PUP(out) = PUP(from);
*out++ = *from++;
} while (--op);
from = out - dist; /* rest from output */
}
@@ -230,14 +211,14 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
if (op < len) { /* some from end of window */
len -= op;
do {
PUP(out) = PUP(from);
*out++ = *from++;
} while (--op);
from = window - OFF;
from = window;
if (wnext < len) { /* some from start of window */
op = wnext;
len -= op;
do {
PUP(out) = PUP(from);
*out++ = *from++;
} while (--op);
from = out - dist; /* rest from output */
}
@@ -248,35 +229,35 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
if (op < len) { /* some from window */
len -= op;
do {
PUP(out) = PUP(from);
*out++ = *from++;
} while (--op);
from = out - dist; /* rest from output */
}
}
while (len > 2) {
PUP(out) = PUP(from);
PUP(out) = PUP(from);
PUP(out) = PUP(from);
*out++ = *from++;
*out++ = *from++;
*out++ = *from++;
len -= 3;
}
if (len) {
PUP(out) = PUP(from);
*out++ = *from++;
if (len > 1)
PUP(out) = PUP(from);
*out++ = *from++;
}
}
else {
from = out - dist; /* copy direct from output */
do { /* minimum length is three */
PUP(out) = PUP(from);
PUP(out) = PUP(from);
PUP(out) = PUP(from);
*out++ = *from++;
*out++ = *from++;
*out++ = *from++;
len -= 3;
} while (len > 2);
if (len) {
PUP(out) = PUP(from);
*out++ = *from++;
if (len > 1)
PUP(out) = PUP(from);
*out++ = *from++;
}
}
}
@@ -313,8 +294,8 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
hold &= (1U << bits) - 1;

/* update state and return */
strm->next_in = in + OFF;
strm->next_out = out + OFF;
strm->next_in = in;
strm->next_out = out;
strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
strm->avail_out = (unsigned)(out < end ?
257 + (end - out) : 257 - (out - end));

1 comment on commit 9aaec95

@chandanbn

This comment has been minimized.

Copy link

commented on 9aaec95 Oct 2, 2018

This is CVE-2016-9841 fix.

Please sign in to comment.
You can’t perform that action at this time.