From: Chin Liang See chin.liang.see@intel.com

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.

Signed-off-by: Mark Adler madler@alumni.caltech.edu Signed-off-by: Chin Liang See chin.liang.see@intel.com Signed-off-by: Jit Loon Lim jit.loon.lim@intel.com --- lib/zlib/inffast.c | 87 ++++++++++++++++++---------------------------- 1 file changed, 34 insertions(+), 53 deletions(-)

diff --git a/lib/zlib/inffast.c b/lib/zlib/inffast.c index e3c7f3b892..a1d617a325 100644 --- a/lib/zlib/inffast.c +++ b/lib/zlib/inffast.c @@ -12,25 +12,6 @@

#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 @@ -97,7 +78,7 @@ void inflate_fast(z_streamp strm, unsigned start)

/* 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); if (in > last && strm->avail_in > 5) { /* @@ -107,7 +88,7 @@ void inflate_fast(z_streamp strm, unsigned start) strm->avail_in = 0xffffffff - (uintptr_t)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 @@ -128,9 +109,9 @@ void inflate_fast(z_streamp strm, unsigned start) 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; } this = lcode[hold & lmask]; @@ -143,14 +124,14 @@ void inflate_fast(z_streamp strm, unsigned start) Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? "inflate: literal '%c'\n" : "inflate: literal 0x%02x\n", this.val)); - PUP(out) = (unsigned char)(this.val); + *out++ = (unsigned char)(this.val); } else if (op & 16) { /* length base */ len = (unsigned)(this.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); @@ -159,9 +140,9 @@ void inflate_fast(z_streamp strm, unsigned start) } 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; } this = dcode[hold & dmask]; @@ -174,10 +155,10 @@ void inflate_fast(z_streamp strm, unsigned start) dist = (unsigned)(this.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; } } @@ -200,13 +181,13 @@ void inflate_fast(z_streamp strm, unsigned start) state->mode = BAD; break; } - from = window - OFF; + from = window; if (write == 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 */ } @@ -217,14 +198,14 @@ void inflate_fast(z_streamp strm, unsigned start) 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 (write < len) { /* some from start of window */ op = write; len -= op; do { - PUP(out) = PUP(from); + *out++ = *from++; } while (--op); from = out - dist; /* rest from output */ } @@ -235,21 +216,21 @@ void inflate_fast(z_streamp strm, unsigned start) 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 { @@ -259,25 +240,25 @@ void inflate_fast(z_streamp strm, unsigned start) from = out - dist; /* copy direct from output */ /* minimum length is three */ /* Align out addr */ - if (!((long)(out - 1 + OFF) & 1)) { - PUP(out) = PUP(from); + if (!((long)(out - 1) & 1)) { + *out++ = *from++; len--; } - sout = (unsigned short *)(out - OFF); + sout = (unsigned short *)(out); if (dist > 2 ) { unsigned short *sfrom;

- sfrom = (unsigned short *)(from - OFF); + sfrom = (unsigned short *)(from); loops = len >> 1; do - PUP(sout) = get_unaligned(++sfrom); + *sout++ = get_unaligned(++sfrom); while (--loops); - out = (unsigned char *)sout + OFF; - from = (unsigned char *)sfrom + OFF; + out = (unsigned char *)sout; + from = (unsigned char *)sfrom; } else { /* dist == 1 or dist == 2 */ unsigned short pat16;

- pat16 = *(sout-2+2*OFF); + pat16 = *(sout-2); if (dist == 1) #if defined(__BIG_ENDIAN) pat16 = (pat16 & 0xff) | ((pat16 & 0xff ) << 8); @@ -288,12 +269,12 @@ void inflate_fast(z_streamp strm, unsigned start) #endif loops = len >> 1; do - PUP(sout) = pat16; + *sout++ = pat16; while (--loops); - out = (unsigned char *)sout + OFF; + out = (unsigned char *)sout; } if (len & 1) - PUP(out) = PUP(from); + *out++ = *from++; } } else if ((op & 64) == 0) { /* 2nd level distance code */ @@ -329,8 +310,8 @@ void inflate_fast(z_streamp strm, unsigned start) 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));