+++ /dev/null
-From 5c44459c3b28a9bd3283aaceab7c615f8020c531 Mon Sep 17 00:00:00 2001
-From: Mark Adler <madler@alumni.caltech.edu>
-Date: Tue, 17 Apr 2018 22:09:22 -0700
-Subject: [PATCH] Fix a bug that can crash deflate on some input when using
- Z_FIXED.
-
-This bug was reported by Danilo Ramos of Eideticom, Inc. It has
-lain in wait 13 years before being found! The bug was introduced
-in zlib 1.2.2.2, with the addition of the Z_FIXED option. That
-option forces the use of fixed Huffman codes. For rare inputs with
-a large number of distant matches, the pending buffer into which
-the compressed data is written can overwrite the distance symbol
-table which it overlays. That results in corrupted output due to
-invalid distances, and can result in out-of-bound accesses,
-crashing the application.
-
-The fix here combines the distance buffer and literal/length
-buffers into a single symbol buffer. Now three bytes of pending
-buffer space are opened up for each literal or length/distance
-pair consumed, instead of the previous two bytes. This assures
-that the pending buffer cannot overwrite the symbol table, since
-the maximum fixed code compressed length/distance is 31 bits, and
-since there are four bytes of pending space for every three bytes
-of symbol space.
----
- deflate.c | 74 ++++++++++++++++++++++++++++++++++++++++---------------
- deflate.h | 25 +++++++++----------
- trees.c | 50 +++++++++++--------------------------
- 3 files changed, 79 insertions(+), 70 deletions(-)
-
-diff --git a/deflate.c b/deflate.c
-index 425babc00..19cba873a 100644
---- a/deflate.c
-+++ b/deflate.c
-@@ -255,11 +255,6 @@ int ZEXPORT deflateInit2_(strm, level, method, windowBits, memLevel, strategy,
- int wrap = 1;
- static const char my_version[] = ZLIB_VERSION;
-
-- ushf *overlay;
-- /* We overlay pending_buf and d_buf+l_buf. This works since the average
-- * output size for (length,distance) codes is <= 24 bits.
-- */
--
- if (version == Z_NULL || version[0] != my_version[0] ||
- stream_size != sizeof(z_stream)) {
- return Z_VERSION_ERROR;
-@@ -329,9 +324,47 @@ int ZEXPORT deflateInit2_(strm, level, method, windowBits, memLevel, strategy,
-
- s->lit_bufsize = 1 << (memLevel + 6); /* 16K elements by default */
-
-- overlay = (ushf *) ZALLOC(strm, s->lit_bufsize, sizeof(ush)+2);
-- s->pending_buf = (uchf *) overlay;
-- s->pending_buf_size = (ulg)s->lit_bufsize * (sizeof(ush)+2L);
-+ /* We overlay pending_buf and sym_buf. This works since the average size
-+ * for length/distance pairs over any compressed block is assured to be 31
-+ * bits or less.
-+ *
-+ * Analysis: The longest fixed codes are a length code of 8 bits plus 5
-+ * extra bits, for lengths 131 to 257. The longest fixed distance codes are
-+ * 5 bits plus 13 extra bits, for distances 16385 to 32768. The longest
-+ * possible fixed-codes length/distance pair is then 31 bits total.
-+ *
-+ * sym_buf starts one-fourth of the way into pending_buf. So there are
-+ * three bytes in sym_buf for every four bytes in pending_buf. Each symbol
-+ * in sym_buf is three bytes -- two for the distance and one for the
-+ * literal/length. As each symbol is consumed, the pointer to the next
-+ * sym_buf value to read moves forward three bytes. From that symbol, up to
-+ * 31 bits are written to pending_buf. The closest the written pending_buf
-+ * bits gets to the next sym_buf symbol to read is just before the last
-+ * code is written. At that time, 31*(n-2) bits have been written, just
-+ * after 24*(n-2) bits have been consumed from sym_buf. sym_buf starts at
-+ * 8*n bits into pending_buf. (Note that the symbol buffer fills when n-1
-+ * symbols are written.) The closest the writing gets to what is unread is
-+ * then n+14 bits. Here n is lit_bufsize, which is 16384 by default, and
-+ * can range from 128 to 32768.
-+ *
-+ * Therefore, at a minimum, there are 142 bits of space between what is
-+ * written and what is read in the overlain buffers, so the symbols cannot
-+ * be overwritten by the compressed data. That space is actually 139 bits,
-+ * due to the three-bit fixed-code block header.
-+ *
-+ * That covers the case where either Z_FIXED is specified, forcing fixed
-+ * codes, or when the use of fixed codes is chosen, because that choice
-+ * results in a smaller compressed block than dynamic codes. That latter
-+ * condition then assures that the above analysis also covers all dynamic
-+ * blocks. A dynamic-code block will only be chosen to be emitted if it has
-+ * fewer bits than a fixed-code block would for the same set of symbols.
-+ * Therefore its average symbol length is assured to be less than 31. So
-+ * the compressed data for a dynamic block also cannot overwrite the
-+ * symbols from which it is being constructed.
-+ */
-+
-+ s->pending_buf = (uchf *) ZALLOC(strm, s->lit_bufsize, 4);
-+ s->pending_buf_size = (ulg)s->lit_bufsize * 4;
-
- if (s->window == Z_NULL || s->prev == Z_NULL || s->head == Z_NULL ||
- s->pending_buf == Z_NULL) {
-@@ -340,8 +373,12 @@ int ZEXPORT deflateInit2_(strm, level, method, windowBits, memLevel, strategy,
- deflateEnd (strm);
- return Z_MEM_ERROR;
- }
-- s->d_buf = overlay + s->lit_bufsize/sizeof(ush);
-- s->l_buf = s->pending_buf + (1+sizeof(ush))*s->lit_bufsize;
-+ s->sym_buf = s->pending_buf + s->lit_bufsize;
-+ s->sym_end = (s->lit_bufsize - 1) * 3;
-+ /* We avoid equality with lit_bufsize*3 because of wraparound at 64K
-+ * on 16 bit machines and because stored blocks are restricted to
-+ * 64K-1 bytes.
-+ */
-
- s->level = level;
- s->strategy = strategy;
-@@ -552,7 +589,7 @@ int ZEXPORT deflatePrime (strm, bits, value)
-
- if (deflateStateCheck(strm)) return Z_STREAM_ERROR;
- s = strm->state;
-- if ((Bytef *)(s->d_buf) < s->pending_out + ((Buf_size + 7) >> 3))
-+ if (s->sym_buf < s->pending_out + ((Buf_size + 7) >> 3))
- return Z_BUF_ERROR;
- do {
- put = Buf_size - s->bi_valid;
-@@ -1113,7 +1150,6 @@ int ZEXPORT deflateCopy (dest, source)
- #else
- deflate_state *ds;
- deflate_state *ss;
-- ushf *overlay;
-
-
- if (deflateStateCheck(source) || dest == Z_NULL) {
-@@ -1133,8 +1169,7 @@ int ZEXPORT deflateCopy (dest, source)
- ds->window = (Bytef *) ZALLOC(dest, ds->w_size, 2*sizeof(Byte));
- ds->prev = (Posf *) ZALLOC(dest, ds->w_size, sizeof(Pos));
- ds->head = (Posf *) ZALLOC(dest, ds->hash_size, sizeof(Pos));
-- overlay = (ushf *) ZALLOC(dest, ds->lit_bufsize, sizeof(ush)+2);
-- ds->pending_buf = (uchf *) overlay;
-+ ds->pending_buf = (uchf *) ZALLOC(dest, ds->lit_bufsize, 4);
-
- if (ds->window == Z_NULL || ds->prev == Z_NULL || ds->head == Z_NULL ||
- ds->pending_buf == Z_NULL) {
-@@ -1148,8 +1183,7 @@ int ZEXPORT deflateCopy (dest, source)
- zmemcpy(ds->pending_buf, ss->pending_buf, (uInt)ds->pending_buf_size);
-
- ds->pending_out = ds->pending_buf + (ss->pending_out - ss->pending_buf);
-- ds->d_buf = overlay + ds->lit_bufsize/sizeof(ush);
-- ds->l_buf = ds->pending_buf + (1+sizeof(ush))*ds->lit_bufsize;
-+ ds->sym_buf = ds->pending_buf + ds->lit_bufsize;
-
- ds->l_desc.dyn_tree = ds->dyn_ltree;
- ds->d_desc.dyn_tree = ds->dyn_dtree;
-@@ -1925,7 +1959,7 @@ local block_state deflate_fast(s, flush)
- FLUSH_BLOCK(s, 1);
- return finish_done;
- }
-- if (s->last_lit)
-+ if (s->sym_next)
- FLUSH_BLOCK(s, 0);
- return block_done;
- }
-@@ -2056,7 +2090,7 @@ local block_state deflate_slow(s, flush)
- FLUSH_BLOCK(s, 1);
- return finish_done;
- }
-- if (s->last_lit)
-+ if (s->sym_next)
- FLUSH_BLOCK(s, 0);
- return block_done;
- }
-@@ -2131,7 +2165,7 @@ local block_state deflate_rle(s, flush)
- FLUSH_BLOCK(s, 1);
- return finish_done;
- }
-- if (s->last_lit)
-+ if (s->sym_next)
- FLUSH_BLOCK(s, 0);
- return block_done;
- }
-@@ -2170,7 +2204,7 @@ local block_state deflate_huff(s, flush)
- FLUSH_BLOCK(s, 1);
- return finish_done;
- }
-- if (s->last_lit)
-+ if (s->sym_next)
- FLUSH_BLOCK(s, 0);
- return block_done;
- }
-diff --git a/deflate.h b/deflate.h
-index 23ecdd312..d4cf1a98b 100644
---- a/deflate.h
-+++ b/deflate.h
-@@ -217,7 +217,7 @@ typedef struct internal_state {
- /* Depth of each subtree used as tie breaker for trees of equal frequency
- */
-
-- uchf *l_buf; /* buffer for literals or lengths */
-+ uchf *sym_buf; /* buffer for distances and literals/lengths */
-
- uInt lit_bufsize;
- /* Size of match buffer for literals/lengths. There are 4 reasons for
-@@ -239,13 +239,8 @@ typedef struct internal_state {
- * - I can't count above 4
- */
-
-- uInt last_lit; /* running index in l_buf */
--
-- ushf *d_buf;
-- /* Buffer for distances. To simplify the code, d_buf and l_buf have
-- * the same number of elements. To use different lengths, an extra flag
-- * array would be necessary.
-- */
-+ uInt sym_next; /* running index in sym_buf */
-+ uInt sym_end; /* symbol table full when sym_next reaches this */
-
- ulg opt_len; /* bit length of current block with optimal trees */
- ulg static_len; /* bit length of current block with static trees */
-@@ -325,20 +320,22 @@ void ZLIB_INTERNAL _tr_stored_block OF((deflate_state *s, charf *buf,
-
- # define _tr_tally_lit(s, c, flush) \
- { uch cc = (c); \
-- s->d_buf[s->last_lit] = 0; \
-- s->l_buf[s->last_lit++] = cc; \
-+ s->sym_buf[s->sym_next++] = 0; \
-+ s->sym_buf[s->sym_next++] = 0; \
-+ s->sym_buf[s->sym_next++] = cc; \
- s->dyn_ltree[cc].Freq++; \
-- flush = (s->last_lit == s->lit_bufsize-1); \
-+ flush = (s->sym_next == s->sym_end); \
- }
- # define _tr_tally_dist(s, distance, length, flush) \
- { uch len = (uch)(length); \
- ush dist = (ush)(distance); \
-- s->d_buf[s->last_lit] = dist; \
-- s->l_buf[s->last_lit++] = len; \
-+ s->sym_buf[s->sym_next++] = dist; \
-+ s->sym_buf[s->sym_next++] = dist >> 8; \
-+ s->sym_buf[s->sym_next++] = len; \
- dist--; \
- s->dyn_ltree[_length_code[len]+LITERALS+1].Freq++; \
- s->dyn_dtree[d_code(dist)].Freq++; \
-- flush = (s->last_lit == s->lit_bufsize-1); \
-+ flush = (s->sym_next == s->sym_end); \
- }
- #else
- # define _tr_tally_lit(s, c, flush) flush = _tr_tally(s, 0, c)
-diff --git a/trees.c b/trees.c
-index 4f4a65011..decaeb7c3 100644
---- a/trees.c
-+++ b/trees.c
-@@ -416,7 +416,7 @@ local void init_block(s)
-
- s->dyn_ltree[END_BLOCK].Freq = 1;
- s->opt_len = s->static_len = 0L;
-- s->last_lit = s->matches = 0;
-+ s->sym_next = s->matches = 0;
- }
-
- #define SMALLEST 1
-@@ -948,7 +948,7 @@ void ZLIB_INTERNAL _tr_flush_block(s, buf, stored_len, last)
-
- Tracev((stderr, "\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u ",
- opt_lenb, s->opt_len, static_lenb, s->static_len, stored_len,
-- s->last_lit));
-+ s->sym_next / 3));
-
- if (static_lenb <= opt_lenb) opt_lenb = static_lenb;
-
-@@ -1017,8 +1017,9 @@ int ZLIB_INTERNAL _tr_tally (s, dist, lc)
- unsigned dist; /* distance of matched string */
- unsigned lc; /* match length-MIN_MATCH or unmatched char (if dist==0) */
- {
-- s->d_buf[s->last_lit] = (ush)dist;
-- s->l_buf[s->last_lit++] = (uch)lc;
-+ s->sym_buf[s->sym_next++] = dist;
-+ s->sym_buf[s->sym_next++] = dist >> 8;
-+ s->sym_buf[s->sym_next++] = lc;
- if (dist == 0) {
- /* lc is the unmatched char */
- s->dyn_ltree[lc].Freq++;
-@@ -1033,30 +1034,7 @@ int ZLIB_INTERNAL _tr_tally (s, dist, lc)
- s->dyn_ltree[_length_code[lc]+LITERALS+1].Freq++;
- s->dyn_dtree[d_code(dist)].Freq++;
- }
--
--#ifdef TRUNCATE_BLOCK
-- /* Try to guess if it is profitable to stop the current block here */
-- if ((s->last_lit & 0x1fff) == 0 && s->level > 2) {
-- /* Compute an upper bound for the compressed length */
-- ulg out_length = (ulg)s->last_lit*8L;
-- ulg in_length = (ulg)((long)s->strstart - s->block_start);
-- int dcode;
-- for (dcode = 0; dcode < D_CODES; dcode++) {
-- out_length += (ulg)s->dyn_dtree[dcode].Freq *
-- (5L+extra_dbits[dcode]);
-- }
-- out_length >>= 3;
-- Tracev((stderr,"\nlast_lit %u, in %ld, out ~%ld(%ld%%) ",
-- s->last_lit, in_length, out_length,
-- 100L - out_length*100L/in_length));
-- if (s->matches < s->last_lit/2 && out_length < in_length/2) return 1;
-- }
--#endif
-- return (s->last_lit == s->lit_bufsize-1);
-- /* We avoid equality with lit_bufsize because of wraparound at 64K
-- * on 16 bit machines and because stored blocks are restricted to
-- * 64K-1 bytes.
-- */
-+ return (s->sym_next == s->sym_end);
- }
-
- /* ===========================================================================
-@@ -1069,13 +1047,14 @@ local void compress_block(s, ltree, dtree)
- {
- unsigned dist; /* distance of matched string */
- int lc; /* match length or unmatched char (if dist == 0) */
-- unsigned lx = 0; /* running index in l_buf */
-+ unsigned sx = 0; /* running index in sym_buf */
- unsigned code; /* the code to send */
- int extra; /* number of extra bits to send */
-
-- if (s->last_lit != 0) do {
-- dist = s->d_buf[lx];
-- lc = s->l_buf[lx++];
-+ if (s->sym_next != 0) do {
-+ dist = s->sym_buf[sx++] & 0xff;
-+ dist += (unsigned)(s->sym_buf[sx++] & 0xff) << 8;
-+ lc = s->sym_buf[sx++];
- if (dist == 0) {
- send_code(s, lc, ltree); /* send a literal byte */
- Tracecv(isgraph(lc), (stderr," '%c' ", lc));
-@@ -1100,11 +1079,10 @@ local void compress_block(s, ltree, dtree)
- }
- } /* literal or match pair ? */
-
-- /* Check that the overlay between pending_buf and d_buf+l_buf is ok: */
-- Assert((uInt)(s->pending) < s->lit_bufsize + 2*lx,
-- "pendingBuf overflow");
-+ /* Check that the overlay between pending_buf and sym_buf is ok: */
-+ Assert(s->pending < s->lit_bufsize + sx, "pendingBuf overflow");
-
-- } while (lx < s->last_lit);
-+ } while (sx < s->sym_next);
-
- send_code(s, END_BLOCK, ltree);
- }
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