| CVE: CVE-2018-25032 |
| Upstream-Status: Backport |
| Signed-off-by: Ross Burton <ross.burton@arm.com> |
| |
| 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); |
| } |