Merge tag 'compress-3.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core

Pull compression update from Greg KH:
 "More fun with the LZO compression code.  Here's some patches that
  properly document what the logic is, and fix up all of the previously
  reported issues against the LZO code.

  This has been in linux-next for a while with no issues"

* tag 'compress-3.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core:
  lzo: check for length overrun in variable length encoding.
  Revert "lzo: properly check for overruns"
  Documentation: lzo: document part of the encoding

1 files changed, 57 insertions, 46 deletions

diff --git a/lib/lzo/lzo1x_decompress_safe.c b/lib/lzo/lzo1x_decompress_safe.c
index 8563081e8da3..a1c387f6afba 100644
--- a/lib/lzo/lzo1x_decompress_safe.c
+++ b/lib/lzo/lzo1x_decompress_safe.c
@@ -19,31 +19,21 @@
 #include <linux/lzo.h>
 #include "lzodefs.h"
 
-#define HAVE_IP(t, x)					\
-	(((size_t)(ip_end - ip) >= (size_t)(t + x)) &&	\
-	 (((t + x) >= t) && ((t + x) >= x)))
+#define HAVE_IP(x)      ((size_t)(ip_end - ip) >= (size_t)(x))
+#define HAVE_OP(x)      ((size_t)(op_end - op) >= (size_t)(x))
+#define NEED_IP(x)      if (!HAVE_IP(x)) goto input_overrun
+#define NEED_OP(x)      if (!HAVE_OP(x)) goto output_overrun
+#define TEST_LB(m_pos)  if ((m_pos) < out) goto lookbehind_overrun
 
-#define HAVE_OP(t, x)					\
-	(((size_t)(op_end - op) >= (size_t)(t + x)) &&	\
-	 (((t + x) >= t) && ((t + x) >= x)))
-
-#define NEED_IP(t, x)					\
-	do {						\
-		if (!HAVE_IP(t, x))			\
-			goto input_overrun;		\
-	} while (0)
-
-#define NEED_OP(t, x)					\
-	do {						\
-		if (!HAVE_OP(t, x))			\
-			goto output_overrun;		\
-	} while (0)
-
-#define TEST_LB(m_pos)					\
-	do {						\
-		if ((m_pos) < out)			\
-			goto lookbehind_overrun;	\
-	} while (0)
+/* This MAX_255_COUNT is the maximum number of times we can add 255 to a base
+ * count without overflowing an integer. The multiply will overflow when
+ * multiplying 255 by more than MAXINT/255. The sum will overflow earlier
+ * depending on the base count. Since the base count is taken from a u8
+ * and a few bits, it is safe to assume that it will always be lower than
+ * or equal to 2*255, thus we can always prevent any overflow by accepting
+ * two less 255 steps. See Documentation/lzo.txt for more information.
+ */
+#define MAX_255_COUNT      ((((size_t)~0) / 255) - 2)
 
 int lzo1x_decompress_safe(const unsigned char *in, size_t in_len,
 			  unsigned char *out, size_t *out_len)
@@ -75,17 +65,24 @@ int lzo1x_decompress_safe(const unsigned char *in, size_t in_len,
 		if (t < 16) {
 			if (likely(state == 0)) {
 				if (unlikely(t == 0)) {
+					size_t offset;
+					const unsigned char *ip_last = ip;
+
 					while (unlikely(*ip == 0)) {
-						t += 255;
 						ip++;
-						NEED_IP(1, 0);
+						NEED_IP(1);
 					}
-					t += 15 + *ip++;
+					offset = ip - ip_last;
+					if (unlikely(offset > MAX_255_COUNT))
+						return LZO_E_ERROR;
+
+					offset = (offset << 8) - offset;
+					t += offset + 15 + *ip++;
 				}
 				t += 3;
 copy_literal_run:
 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
-				if (likely(HAVE_IP(t, 15) && HAVE_OP(t, 15))) {
+				if (likely(HAVE_IP(t + 15) && HAVE_OP(t + 15))) {
 					const unsigned char *ie = ip + t;
 					unsigned char *oe = op + t;
 					do {
@@ -101,8 +98,8 @@ copy_literal_run:
 				} else
 #endif
 				{
-					NEED_OP(t, 0);
-					NEED_IP(t, 3);
+					NEED_OP(t);
+					NEED_IP(t + 3);
 					do {
 						*op++ = *ip++;
 					} while (--t > 0);
@@ -115,7 +112,7 @@ copy_literal_run:
 				m_pos -= t >> 2;
 				m_pos -= *ip++ << 2;
 				TEST_LB(m_pos);
-				NEED_OP(2, 0);
+				NEED_OP(2);
 				op[0] = m_pos[0];
 				op[1] = m_pos[1];
 				op += 2;
@@ -136,13 +133,20 @@ copy_literal_run:
 		} else if (t >= 32) {
 			t = (t & 31) + (3 - 1);
 			if (unlikely(t == 2)) {
+				size_t offset;
+				const unsigned char *ip_last = ip;
+
 				while (unlikely(*ip == 0)) {
-					t += 255;
 					ip++;
-					NEED_IP(1, 0);
+					NEED_IP(1);
 				}
-				t += 31 + *ip++;
-				NEED_IP(2, 0);
+				offset = ip - ip_last;
+				if (unlikely(offset > MAX_255_COUNT))
+					return LZO_E_ERROR;
+
+				offset = (offset << 8) - offset;
+				t += offset + 31 + *ip++;
+				NEED_IP(2);
 			}
 			m_pos = op - 1;
 			next = get_unaligned_le16(ip);
@@ -154,13 +158,20 @@ copy_literal_run:
 			m_pos -= (t & 8) << 11;
 			t = (t & 7) + (3 - 1);
 			if (unlikely(t == 2)) {
+				size_t offset;
+				const unsigned char *ip_last = ip;
+
 				while (unlikely(*ip == 0)) {
-					t += 255;
 					ip++;
-					NEED_IP(1, 0);
+					NEED_IP(1);
 				}
-				t += 7 + *ip++;
-				NEED_IP(2, 0);
+				offset = ip - ip_last;
+				if (unlikely(offset > MAX_255_COUNT))
+					return LZO_E_ERROR;
+
+				offset = (offset << 8) - offset;
+				t += offset + 7 + *ip++;
+				NEED_IP(2);
 			}
 			next = get_unaligned_le16(ip);
 			ip += 2;
@@ -174,7 +185,7 @@ copy_literal_run:
 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
 		if (op - m_pos >= 8) {
 			unsigned char *oe = op + t;
-			if (likely(HAVE_OP(t, 15))) {
+			if (likely(HAVE_OP(t + 15))) {
 				do {
 					COPY8(op, m_pos);
 					op += 8;
@@ -184,7 +195,7 @@ copy_literal_run:
 					m_pos += 8;
 				} while (op < oe);
 				op = oe;
-				if (HAVE_IP(6, 0)) {
+				if (HAVE_IP(6)) {
 					state = next;
 					COPY4(op, ip);
 					op += next;
@@ -192,7 +203,7 @@ copy_literal_run:
 					continue;
 				}
 			} else {
-				NEED_OP(t, 0);
+				NEED_OP(t);
 				do {
 					*op++ = *m_pos++;
 				} while (op < oe);
@@ -201,7 +212,7 @@ copy_literal_run:
 #endif
 		{
 			unsigned char *oe = op + t;
-			NEED_OP(t, 0);
+			NEED_OP(t);
 			op[0] = m_pos[0];
 			op[1] = m_pos[1];
 			op += 2;
@@ -214,15 +225,15 @@ match_next:
 		state = next;
 		t = next;
 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
-		if (likely(HAVE_IP(6, 0) && HAVE_OP(4, 0))) {
+		if (likely(HAVE_IP(6) && HAVE_OP(4))) {
 			COPY4(op, ip);
 			op += t;
 			ip += t;
 		} else
 #endif
 		{
-			NEED_IP(t, 3);
-			NEED_OP(t, 0);
+			NEED_IP(t + 3);
+			NEED_OP(t);
 			while (t > 0) {
 				*op++ = *ip++;
 				t--;