Andrew Geissler | 9aee500 | 2022-03-30 16:27:02 +0000 | [diff] [blame^] | 1 | CVE: CVE-2018-25032 |
| 2 | Upstream-Status: Backport |
| 3 | Signed-off-by: Ross Burton <ross.burton@arm.com> |
| 4 | |
| 5 | From 5c44459c3b28a9bd3283aaceab7c615f8020c531 Mon Sep 17 00:00:00 2001 |
| 6 | From: Mark Adler <madler@alumni.caltech.edu> |
| 7 | Date: Tue, 17 Apr 2018 22:09:22 -0700 |
| 8 | Subject: [PATCH] Fix a bug that can crash deflate on some input when using |
| 9 | Z_FIXED. |
| 10 | |
| 11 | This bug was reported by Danilo Ramos of Eideticom, Inc. It has |
| 12 | lain in wait 13 years before being found! The bug was introduced |
| 13 | in zlib 1.2.2.2, with the addition of the Z_FIXED option. That |
| 14 | option forces the use of fixed Huffman codes. For rare inputs with |
| 15 | a large number of distant matches, the pending buffer into which |
| 16 | the compressed data is written can overwrite the distance symbol |
| 17 | table which it overlays. That results in corrupted output due to |
| 18 | invalid distances, and can result in out-of-bound accesses, |
| 19 | crashing the application. |
| 20 | |
| 21 | The fix here combines the distance buffer and literal/length |
| 22 | buffers into a single symbol buffer. Now three bytes of pending |
| 23 | buffer space are opened up for each literal or length/distance |
| 24 | pair consumed, instead of the previous two bytes. This assures |
| 25 | that the pending buffer cannot overwrite the symbol table, since |
| 26 | the maximum fixed code compressed length/distance is 31 bits, and |
| 27 | since there are four bytes of pending space for every three bytes |
| 28 | of symbol space. |
| 29 | --- |
| 30 | deflate.c | 74 ++++++++++++++++++++++++++++++++++++++++--------------- |
| 31 | deflate.h | 25 +++++++++---------- |
| 32 | trees.c | 50 +++++++++++-------------------------- |
| 33 | 3 files changed, 79 insertions(+), 70 deletions(-) |
| 34 | |
| 35 | diff --git a/deflate.c b/deflate.c |
| 36 | index 425babc00..19cba873a 100644 |
| 37 | --- a/deflate.c |
| 38 | +++ b/deflate.c |
| 39 | @@ -255,11 +255,6 @@ int ZEXPORT deflateInit2_(strm, level, method, windowBits, memLevel, strategy, |
| 40 | int wrap = 1; |
| 41 | static const char my_version[] = ZLIB_VERSION; |
| 42 | |
| 43 | - ushf *overlay; |
| 44 | - /* We overlay pending_buf and d_buf+l_buf. This works since the average |
| 45 | - * output size for (length,distance) codes is <= 24 bits. |
| 46 | - */ |
| 47 | - |
| 48 | if (version == Z_NULL || version[0] != my_version[0] || |
| 49 | stream_size != sizeof(z_stream)) { |
| 50 | return Z_VERSION_ERROR; |
| 51 | @@ -329,9 +324,47 @@ int ZEXPORT deflateInit2_(strm, level, method, windowBits, memLevel, strategy, |
| 52 | |
| 53 | s->lit_bufsize = 1 << (memLevel + 6); /* 16K elements by default */ |
| 54 | |
| 55 | - overlay = (ushf *) ZALLOC(strm, s->lit_bufsize, sizeof(ush)+2); |
| 56 | - s->pending_buf = (uchf *) overlay; |
| 57 | - s->pending_buf_size = (ulg)s->lit_bufsize * (sizeof(ush)+2L); |
| 58 | + /* We overlay pending_buf and sym_buf. This works since the average size |
| 59 | + * for length/distance pairs over any compressed block is assured to be 31 |
| 60 | + * bits or less. |
| 61 | + * |
| 62 | + * Analysis: The longest fixed codes are a length code of 8 bits plus 5 |
| 63 | + * extra bits, for lengths 131 to 257. The longest fixed distance codes are |
| 64 | + * 5 bits plus 13 extra bits, for distances 16385 to 32768. The longest |
| 65 | + * possible fixed-codes length/distance pair is then 31 bits total. |
| 66 | + * |
| 67 | + * sym_buf starts one-fourth of the way into pending_buf. So there are |
| 68 | + * three bytes in sym_buf for every four bytes in pending_buf. Each symbol |
| 69 | + * in sym_buf is three bytes -- two for the distance and one for the |
| 70 | + * literal/length. As each symbol is consumed, the pointer to the next |
| 71 | + * sym_buf value to read moves forward three bytes. From that symbol, up to |
| 72 | + * 31 bits are written to pending_buf. The closest the written pending_buf |
| 73 | + * bits gets to the next sym_buf symbol to read is just before the last |
| 74 | + * code is written. At that time, 31*(n-2) bits have been written, just |
| 75 | + * after 24*(n-2) bits have been consumed from sym_buf. sym_buf starts at |
| 76 | + * 8*n bits into pending_buf. (Note that the symbol buffer fills when n-1 |
| 77 | + * symbols are written.) The closest the writing gets to what is unread is |
| 78 | + * then n+14 bits. Here n is lit_bufsize, which is 16384 by default, and |
| 79 | + * can range from 128 to 32768. |
| 80 | + * |
| 81 | + * Therefore, at a minimum, there are 142 bits of space between what is |
| 82 | + * written and what is read in the overlain buffers, so the symbols cannot |
| 83 | + * be overwritten by the compressed data. That space is actually 139 bits, |
| 84 | + * due to the three-bit fixed-code block header. |
| 85 | + * |
| 86 | + * That covers the case where either Z_FIXED is specified, forcing fixed |
| 87 | + * codes, or when the use of fixed codes is chosen, because that choice |
| 88 | + * results in a smaller compressed block than dynamic codes. That latter |
| 89 | + * condition then assures that the above analysis also covers all dynamic |
| 90 | + * blocks. A dynamic-code block will only be chosen to be emitted if it has |
| 91 | + * fewer bits than a fixed-code block would for the same set of symbols. |
| 92 | + * Therefore its average symbol length is assured to be less than 31. So |
| 93 | + * the compressed data for a dynamic block also cannot overwrite the |
| 94 | + * symbols from which it is being constructed. |
| 95 | + */ |
| 96 | + |
| 97 | + s->pending_buf = (uchf *) ZALLOC(strm, s->lit_bufsize, 4); |
| 98 | + s->pending_buf_size = (ulg)s->lit_bufsize * 4; |
| 99 | |
| 100 | if (s->window == Z_NULL || s->prev == Z_NULL || s->head == Z_NULL || |
| 101 | s->pending_buf == Z_NULL) { |
| 102 | @@ -340,8 +373,12 @@ int ZEXPORT deflateInit2_(strm, level, method, windowBits, memLevel, strategy, |
| 103 | deflateEnd (strm); |
| 104 | return Z_MEM_ERROR; |
| 105 | } |
| 106 | - s->d_buf = overlay + s->lit_bufsize/sizeof(ush); |
| 107 | - s->l_buf = s->pending_buf + (1+sizeof(ush))*s->lit_bufsize; |
| 108 | + s->sym_buf = s->pending_buf + s->lit_bufsize; |
| 109 | + s->sym_end = (s->lit_bufsize - 1) * 3; |
| 110 | + /* We avoid equality with lit_bufsize*3 because of wraparound at 64K |
| 111 | + * on 16 bit machines and because stored blocks are restricted to |
| 112 | + * 64K-1 bytes. |
| 113 | + */ |
| 114 | |
| 115 | s->level = level; |
| 116 | s->strategy = strategy; |
| 117 | @@ -552,7 +589,7 @@ int ZEXPORT deflatePrime (strm, bits, value) |
| 118 | |
| 119 | if (deflateStateCheck(strm)) return Z_STREAM_ERROR; |
| 120 | s = strm->state; |
| 121 | - if ((Bytef *)(s->d_buf) < s->pending_out + ((Buf_size + 7) >> 3)) |
| 122 | + if (s->sym_buf < s->pending_out + ((Buf_size + 7) >> 3)) |
| 123 | return Z_BUF_ERROR; |
| 124 | do { |
| 125 | put = Buf_size - s->bi_valid; |
| 126 | @@ -1113,7 +1150,6 @@ int ZEXPORT deflateCopy (dest, source) |
| 127 | #else |
| 128 | deflate_state *ds; |
| 129 | deflate_state *ss; |
| 130 | - ushf *overlay; |
| 131 | |
| 132 | |
| 133 | if (deflateStateCheck(source) || dest == Z_NULL) { |
| 134 | @@ -1133,8 +1169,7 @@ int ZEXPORT deflateCopy (dest, source) |
| 135 | ds->window = (Bytef *) ZALLOC(dest, ds->w_size, 2*sizeof(Byte)); |
| 136 | ds->prev = (Posf *) ZALLOC(dest, ds->w_size, sizeof(Pos)); |
| 137 | ds->head = (Posf *) ZALLOC(dest, ds->hash_size, sizeof(Pos)); |
| 138 | - overlay = (ushf *) ZALLOC(dest, ds->lit_bufsize, sizeof(ush)+2); |
| 139 | - ds->pending_buf = (uchf *) overlay; |
| 140 | + ds->pending_buf = (uchf *) ZALLOC(dest, ds->lit_bufsize, 4); |
| 141 | |
| 142 | if (ds->window == Z_NULL || ds->prev == Z_NULL || ds->head == Z_NULL || |
| 143 | ds->pending_buf == Z_NULL) { |
| 144 | @@ -1148,8 +1183,7 @@ int ZEXPORT deflateCopy (dest, source) |
| 145 | zmemcpy(ds->pending_buf, ss->pending_buf, (uInt)ds->pending_buf_size); |
| 146 | |
| 147 | ds->pending_out = ds->pending_buf + (ss->pending_out - ss->pending_buf); |
| 148 | - ds->d_buf = overlay + ds->lit_bufsize/sizeof(ush); |
| 149 | - ds->l_buf = ds->pending_buf + (1+sizeof(ush))*ds->lit_bufsize; |
| 150 | + ds->sym_buf = ds->pending_buf + ds->lit_bufsize; |
| 151 | |
| 152 | ds->l_desc.dyn_tree = ds->dyn_ltree; |
| 153 | ds->d_desc.dyn_tree = ds->dyn_dtree; |
| 154 | @@ -1925,7 +1959,7 @@ local block_state deflate_fast(s, flush) |
| 155 | FLUSH_BLOCK(s, 1); |
| 156 | return finish_done; |
| 157 | } |
| 158 | - if (s->last_lit) |
| 159 | + if (s->sym_next) |
| 160 | FLUSH_BLOCK(s, 0); |
| 161 | return block_done; |
| 162 | } |
| 163 | @@ -2056,7 +2090,7 @@ local block_state deflate_slow(s, flush) |
| 164 | FLUSH_BLOCK(s, 1); |
| 165 | return finish_done; |
| 166 | } |
| 167 | - if (s->last_lit) |
| 168 | + if (s->sym_next) |
| 169 | FLUSH_BLOCK(s, 0); |
| 170 | return block_done; |
| 171 | } |
| 172 | @@ -2131,7 +2165,7 @@ local block_state deflate_rle(s, flush) |
| 173 | FLUSH_BLOCK(s, 1); |
| 174 | return finish_done; |
| 175 | } |
| 176 | - if (s->last_lit) |
| 177 | + if (s->sym_next) |
| 178 | FLUSH_BLOCK(s, 0); |
| 179 | return block_done; |
| 180 | } |
| 181 | @@ -2170,7 +2204,7 @@ local block_state deflate_huff(s, flush) |
| 182 | FLUSH_BLOCK(s, 1); |
| 183 | return finish_done; |
| 184 | } |
| 185 | - if (s->last_lit) |
| 186 | + if (s->sym_next) |
| 187 | FLUSH_BLOCK(s, 0); |
| 188 | return block_done; |
| 189 | } |
| 190 | diff --git a/deflate.h b/deflate.h |
| 191 | index 23ecdd312..d4cf1a98b 100644 |
| 192 | --- a/deflate.h |
| 193 | +++ b/deflate.h |
| 194 | @@ -217,7 +217,7 @@ typedef struct internal_state { |
| 195 | /* Depth of each subtree used as tie breaker for trees of equal frequency |
| 196 | */ |
| 197 | |
| 198 | - uchf *l_buf; /* buffer for literals or lengths */ |
| 199 | + uchf *sym_buf; /* buffer for distances and literals/lengths */ |
| 200 | |
| 201 | uInt lit_bufsize; |
| 202 | /* Size of match buffer for literals/lengths. There are 4 reasons for |
| 203 | @@ -239,13 +239,8 @@ typedef struct internal_state { |
| 204 | * - I can't count above 4 |
| 205 | */ |
| 206 | |
| 207 | - uInt last_lit; /* running index in l_buf */ |
| 208 | - |
| 209 | - ushf *d_buf; |
| 210 | - /* Buffer for distances. To simplify the code, d_buf and l_buf have |
| 211 | - * the same number of elements. To use different lengths, an extra flag |
| 212 | - * array would be necessary. |
| 213 | - */ |
| 214 | + uInt sym_next; /* running index in sym_buf */ |
| 215 | + uInt sym_end; /* symbol table full when sym_next reaches this */ |
| 216 | |
| 217 | ulg opt_len; /* bit length of current block with optimal trees */ |
| 218 | ulg static_len; /* bit length of current block with static trees */ |
| 219 | @@ -325,20 +320,22 @@ void ZLIB_INTERNAL _tr_stored_block OF((deflate_state *s, charf *buf, |
| 220 | |
| 221 | # define _tr_tally_lit(s, c, flush) \ |
| 222 | { uch cc = (c); \ |
| 223 | - s->d_buf[s->last_lit] = 0; \ |
| 224 | - s->l_buf[s->last_lit++] = cc; \ |
| 225 | + s->sym_buf[s->sym_next++] = 0; \ |
| 226 | + s->sym_buf[s->sym_next++] = 0; \ |
| 227 | + s->sym_buf[s->sym_next++] = cc; \ |
| 228 | s->dyn_ltree[cc].Freq++; \ |
| 229 | - flush = (s->last_lit == s->lit_bufsize-1); \ |
| 230 | + flush = (s->sym_next == s->sym_end); \ |
| 231 | } |
| 232 | # define _tr_tally_dist(s, distance, length, flush) \ |
| 233 | { uch len = (uch)(length); \ |
| 234 | ush dist = (ush)(distance); \ |
| 235 | - s->d_buf[s->last_lit] = dist; \ |
| 236 | - s->l_buf[s->last_lit++] = len; \ |
| 237 | + s->sym_buf[s->sym_next++] = dist; \ |
| 238 | + s->sym_buf[s->sym_next++] = dist >> 8; \ |
| 239 | + s->sym_buf[s->sym_next++] = len; \ |
| 240 | dist--; \ |
| 241 | s->dyn_ltree[_length_code[len]+LITERALS+1].Freq++; \ |
| 242 | s->dyn_dtree[d_code(dist)].Freq++; \ |
| 243 | - flush = (s->last_lit == s->lit_bufsize-1); \ |
| 244 | + flush = (s->sym_next == s->sym_end); \ |
| 245 | } |
| 246 | #else |
| 247 | # define _tr_tally_lit(s, c, flush) flush = _tr_tally(s, 0, c) |
| 248 | diff --git a/trees.c b/trees.c |
| 249 | index 4f4a65011..decaeb7c3 100644 |
| 250 | --- a/trees.c |
| 251 | +++ b/trees.c |
| 252 | @@ -416,7 +416,7 @@ local void init_block(s) |
| 253 | |
| 254 | s->dyn_ltree[END_BLOCK].Freq = 1; |
| 255 | s->opt_len = s->static_len = 0L; |
| 256 | - s->last_lit = s->matches = 0; |
| 257 | + s->sym_next = s->matches = 0; |
| 258 | } |
| 259 | |
| 260 | #define SMALLEST 1 |
| 261 | @@ -948,7 +948,7 @@ void ZLIB_INTERNAL _tr_flush_block(s, buf, stored_len, last) |
| 262 | |
| 263 | Tracev((stderr, "\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u ", |
| 264 | opt_lenb, s->opt_len, static_lenb, s->static_len, stored_len, |
| 265 | - s->last_lit)); |
| 266 | + s->sym_next / 3)); |
| 267 | |
| 268 | if (static_lenb <= opt_lenb) opt_lenb = static_lenb; |
| 269 | |
| 270 | @@ -1017,8 +1017,9 @@ int ZLIB_INTERNAL _tr_tally (s, dist, lc) |
| 271 | unsigned dist; /* distance of matched string */ |
| 272 | unsigned lc; /* match length-MIN_MATCH or unmatched char (if dist==0) */ |
| 273 | { |
| 274 | - s->d_buf[s->last_lit] = (ush)dist; |
| 275 | - s->l_buf[s->last_lit++] = (uch)lc; |
| 276 | + s->sym_buf[s->sym_next++] = dist; |
| 277 | + s->sym_buf[s->sym_next++] = dist >> 8; |
| 278 | + s->sym_buf[s->sym_next++] = lc; |
| 279 | if (dist == 0) { |
| 280 | /* lc is the unmatched char */ |
| 281 | s->dyn_ltree[lc].Freq++; |
| 282 | @@ -1033,30 +1034,7 @@ int ZLIB_INTERNAL _tr_tally (s, dist, lc) |
| 283 | s->dyn_ltree[_length_code[lc]+LITERALS+1].Freq++; |
| 284 | s->dyn_dtree[d_code(dist)].Freq++; |
| 285 | } |
| 286 | - |
| 287 | -#ifdef TRUNCATE_BLOCK |
| 288 | - /* Try to guess if it is profitable to stop the current block here */ |
| 289 | - if ((s->last_lit & 0x1fff) == 0 && s->level > 2) { |
| 290 | - /* Compute an upper bound for the compressed length */ |
| 291 | - ulg out_length = (ulg)s->last_lit*8L; |
| 292 | - ulg in_length = (ulg)((long)s->strstart - s->block_start); |
| 293 | - int dcode; |
| 294 | - for (dcode = 0; dcode < D_CODES; dcode++) { |
| 295 | - out_length += (ulg)s->dyn_dtree[dcode].Freq * |
| 296 | - (5L+extra_dbits[dcode]); |
| 297 | - } |
| 298 | - out_length >>= 3; |
| 299 | - Tracev((stderr,"\nlast_lit %u, in %ld, out ~%ld(%ld%%) ", |
| 300 | - s->last_lit, in_length, out_length, |
| 301 | - 100L - out_length*100L/in_length)); |
| 302 | - if (s->matches < s->last_lit/2 && out_length < in_length/2) return 1; |
| 303 | - } |
| 304 | -#endif |
| 305 | - return (s->last_lit == s->lit_bufsize-1); |
| 306 | - /* We avoid equality with lit_bufsize because of wraparound at 64K |
| 307 | - * on 16 bit machines and because stored blocks are restricted to |
| 308 | - * 64K-1 bytes. |
| 309 | - */ |
| 310 | + return (s->sym_next == s->sym_end); |
| 311 | } |
| 312 | |
| 313 | /* =========================================================================== |
| 314 | @@ -1069,13 +1047,14 @@ local void compress_block(s, ltree, dtree) |
| 315 | { |
| 316 | unsigned dist; /* distance of matched string */ |
| 317 | int lc; /* match length or unmatched char (if dist == 0) */ |
| 318 | - unsigned lx = 0; /* running index in l_buf */ |
| 319 | + unsigned sx = 0; /* running index in sym_buf */ |
| 320 | unsigned code; /* the code to send */ |
| 321 | int extra; /* number of extra bits to send */ |
| 322 | |
| 323 | - if (s->last_lit != 0) do { |
| 324 | - dist = s->d_buf[lx]; |
| 325 | - lc = s->l_buf[lx++]; |
| 326 | + if (s->sym_next != 0) do { |
| 327 | + dist = s->sym_buf[sx++] & 0xff; |
| 328 | + dist += (unsigned)(s->sym_buf[sx++] & 0xff) << 8; |
| 329 | + lc = s->sym_buf[sx++]; |
| 330 | if (dist == 0) { |
| 331 | send_code(s, lc, ltree); /* send a literal byte */ |
| 332 | Tracecv(isgraph(lc), (stderr," '%c' ", lc)); |
| 333 | @@ -1100,11 +1079,10 @@ local void compress_block(s, ltree, dtree) |
| 334 | } |
| 335 | } /* literal or match pair ? */ |
| 336 | |
| 337 | - /* Check that the overlay between pending_buf and d_buf+l_buf is ok: */ |
| 338 | - Assert((uInt)(s->pending) < s->lit_bufsize + 2*lx, |
| 339 | - "pendingBuf overflow"); |
| 340 | + /* Check that the overlay between pending_buf and sym_buf is ok: */ |
| 341 | + Assert(s->pending < s->lit_bufsize + sx, "pendingBuf overflow"); |
| 342 | |
| 343 | - } while (lx < s->last_lit); |
| 344 | + } while (sx < s->sym_next); |
| 345 | |
| 346 | send_code(s, END_BLOCK, ltree); |
| 347 | } |