1 /*
2  * XZ decompressor
3  *
4  * Authors: Lasse Collin <lasse.collin@tukaani.org>
5  *          Igor Pavlov <https://7-zip.org/>
6  *
7  * This file has been put into the public domain.
8  * You can do whatever you want with this file.
9  */
10 
11 #ifndef XZ_H
12 #define XZ_H
13 
14 #ifdef __KERNEL__
15 #	include <linux/stddef.h>
16 #	include <linux/types.h>
17 #else
18 #	include <stddef.h>
19 #	include <stdint.h>
20 #endif
21 
22 /* In Linux, this is used to make extern functions static when needed. */
23 #ifndef XZ_EXTERN
24 #	define XZ_EXTERN extern
25 #endif
26 
27 /**
28  * enum xz_mode - Operation mode
29  *
30  * @XZ_SINGLE:              Single-call mode. This uses less RAM than
31  *                          multi-call modes, because the LZMA2
32  *                          dictionary doesn't need to be allocated as
33  *                          part of the decoder state. All required data
34  *                          structures are allocated at initialization,
35  *                          so xz_dec_run() cannot return XZ_MEM_ERROR.
36  * @XZ_PREALLOC:            Multi-call mode with preallocated LZMA2
37  *                          dictionary buffer. All data structures are
38  *                          allocated at initialization, so xz_dec_run()
39  *                          cannot return XZ_MEM_ERROR.
40  * @XZ_DYNALLOC:            Multi-call mode. The LZMA2 dictionary is
41  *                          allocated once the required size has been
42  *                          parsed from the stream headers. If the
43  *                          allocation fails, xz_dec_run() will return
44  *                          XZ_MEM_ERROR.
45  *
46  * It is possible to enable support only for a subset of the above
47  * modes at compile time by defining XZ_DEC_SINGLE, XZ_DEC_PREALLOC,
48  * or XZ_DEC_DYNALLOC. The xz_dec kernel module is always compiled
49  * with support for all operation modes, but the preboot code may
50  * be built with fewer features to minimize code size.
51  */
52 enum xz_mode {
53 	XZ_SINGLE,
54 	XZ_PREALLOC,
55 	XZ_DYNALLOC
56 };
57 
58 /**
59  * enum xz_ret - Return codes
60  * @XZ_OK:                  Everything is OK so far. More input or more
61  *                          output space is required to continue. This
62  *                          return code is possible only in multi-call mode
63  *                          (XZ_PREALLOC or XZ_DYNALLOC).
64  * @XZ_STREAM_END:          Operation finished successfully.
65  * @XZ_UNSUPPORTED_CHECK:   Integrity check type is not supported. Decoding
66  *                          is still possible in multi-call mode by simply
67  *                          calling xz_dec_run() again.
68  *                          Note that this return value is used only if
69  *                          XZ_DEC_ANY_CHECK was defined at build time,
70  *                          which is not used in the kernel. Unsupported
71  *                          check types return XZ_OPTIONS_ERROR if
72  *                          XZ_DEC_ANY_CHECK was not defined at build time.
73  * @XZ_MEM_ERROR:           Allocating memory failed. This return code is
74  *                          possible only if the decoder was initialized
75  *                          with XZ_DYNALLOC. The amount of memory that was
76  *                          tried to be allocated was no more than the
77  *                          dict_max argument given to xz_dec_init().
78  * @XZ_MEMLIMIT_ERROR:      A bigger LZMA2 dictionary would be needed than
79  *                          allowed by the dict_max argument given to
80  *                          xz_dec_init(). This return value is possible
81  *                          only in multi-call mode (XZ_PREALLOC or
82  *                          XZ_DYNALLOC); the single-call mode (XZ_SINGLE)
83  *                          ignores the dict_max argument.
84  * @XZ_FORMAT_ERROR:        File format was not recognized (wrong magic
85  *                          bytes).
86  * @XZ_OPTIONS_ERROR:       This implementation doesn't support the requested
87  *                          compression options. In the decoder this means
88  *                          that the header CRC32 matches, but the header
89  *                          itself specifies something that we don't support.
90  * @XZ_DATA_ERROR:          Compressed data is corrupt.
91  * @XZ_BUF_ERROR:           Cannot make any progress. Details are slightly
92  *                          different between multi-call and single-call
93  *                          mode; more information below.
94  *
95  * In multi-call mode, XZ_BUF_ERROR is returned when two consecutive calls
96  * to XZ code cannot consume any input and cannot produce any new output.
97  * This happens when there is no new input available, or the output buffer
98  * is full while at least one output byte is still pending. Assuming your
99  * code is not buggy, you can get this error only when decoding a compressed
100  * stream that is truncated or otherwise corrupt.
101  *
102  * In single-call mode, XZ_BUF_ERROR is returned only when the output buffer
103  * is too small or the compressed input is corrupt in a way that makes the
104  * decoder produce more output than the caller expected. When it is
105  * (relatively) clear that the compressed input is truncated, XZ_DATA_ERROR
106  * is used instead of XZ_BUF_ERROR.
107  */
108 enum xz_ret {
109 	XZ_OK,
110 	XZ_STREAM_END,
111 	XZ_UNSUPPORTED_CHECK,
112 	XZ_MEM_ERROR,
113 	XZ_MEMLIMIT_ERROR,
114 	XZ_FORMAT_ERROR,
115 	XZ_OPTIONS_ERROR,
116 	XZ_DATA_ERROR,
117 	XZ_BUF_ERROR
118 };
119 
120 /**
121  * struct xz_buf - Passing input and output buffers to XZ code
122  * @in:         Beginning of the input buffer. This may be NULL if and only
123  *              if in_pos is equal to in_size.
124  * @in_pos:     Current position in the input buffer. This must not exceed
125  *              in_size.
126  * @in_size:    Size of the input buffer
127  * @out:        Beginning of the output buffer. This may be NULL if and only
128  *              if out_pos is equal to out_size.
129  * @out_pos:    Current position in the output buffer. This must not exceed
130  *              out_size.
131  * @out_size:   Size of the output buffer
132  *
133  * Only the contents of the output buffer from out[out_pos] onward, and
134  * the variables in_pos and out_pos are modified by the XZ code.
135  */
136 struct xz_buf {
137 	const uint8_t *in;
138 	size_t in_pos;
139 	size_t in_size;
140 
141 	uint8_t *out;
142 	size_t out_pos;
143 	size_t out_size;
144 };
145 
146 /**
147  * struct xz_dec - Opaque type to hold the XZ decoder state
148  */
149 struct xz_dec;
150 
151 /**
152  * xz_dec_init() - Allocate and initialize a XZ decoder state
153  * @mode:       Operation mode
154  * @dict_max:   Maximum size of the LZMA2 dictionary (history buffer) for
155  *              multi-call decoding. This is ignored in single-call mode
156  *              (mode == XZ_SINGLE). LZMA2 dictionary is always 2^n bytes
157  *              or 2^n + 2^(n-1) bytes (the latter sizes are less common
158  *              in practice), so other values for dict_max don't make sense.
159  *              In the kernel, dictionary sizes of 64 KiB, 128 KiB, 256 KiB,
160  *              512 KiB, and 1 MiB are probably the only reasonable values,
161  *              except for kernel and initramfs images where a bigger
162  *              dictionary can be fine and useful.
163  *
164  * Single-call mode (XZ_SINGLE): xz_dec_run() decodes the whole stream at
165  * once. The caller must provide enough output space or the decoding will
166  * fail. The output space is used as the dictionary buffer, which is why
167  * there is no need to allocate the dictionary as part of the decoder's
168  * internal state.
169  *
170  * Because the output buffer is used as the workspace, streams encoded using
171  * a big dictionary are not a problem in single-call mode. It is enough that
172  * the output buffer is big enough to hold the actual uncompressed data; it
173  * can be smaller than the dictionary size stored in the stream headers.
174  *
175  * Multi-call mode with preallocated dictionary (XZ_PREALLOC): dict_max bytes
176  * of memory is preallocated for the LZMA2 dictionary. This way there is no
177  * risk that xz_dec_run() could run out of memory, since xz_dec_run() will
178  * never allocate any memory. Instead, if the preallocated dictionary is too
179  * small for decoding the given input stream, xz_dec_run() will return
180  * XZ_MEMLIMIT_ERROR. Thus, it is important to know what kind of data will be
181  * decoded to avoid allocating excessive amount of memory for the dictionary.
182  *
183  * Multi-call mode with dynamically allocated dictionary (XZ_DYNALLOC):
184  * dict_max specifies the maximum allowed dictionary size that xz_dec_run()
185  * may allocate once it has parsed the dictionary size from the stream
186  * headers. This way excessive allocations can be avoided while still
187  * limiting the maximum memory usage to a sane value to prevent running the
188  * system out of memory when decompressing streams from untrusted sources.
189  *
190  * On success, xz_dec_init() returns a pointer to struct xz_dec, which is
191  * ready to be used with xz_dec_run(). If memory allocation fails,
192  * xz_dec_init() returns NULL.
193  */
194 XZ_EXTERN struct xz_dec *xz_dec_init(enum xz_mode mode, uint32_t dict_max);
195 
196 /**
197  * xz_dec_run() - Run the XZ decoder
198  * @s:          Decoder state allocated using xz_dec_init()
199  * @b:          Input and output buffers
200  *
201  * The possible return values depend on build options and operation mode.
202  * See enum xz_ret for details.
203  *
204  * Note that if an error occurs in single-call mode (return value is not
205  * XZ_STREAM_END), b->in_pos and b->out_pos are not modified and the
206  * contents of the output buffer from b->out[b->out_pos] onward are
207  * undefined. This is true even after XZ_BUF_ERROR, because with some filter
208  * chains, there may be a second pass over the output buffer, and this pass
209  * cannot be properly done if the output buffer is truncated. Thus, you
210  * cannot give the single-call decoder a too small buffer and then expect to
211  * get that amount valid data from the beginning of the stream. You must use
212  * the multi-call decoder if you don't want to uncompress the whole stream.
213  */
214 XZ_EXTERN enum xz_ret xz_dec_run(struct xz_dec *s, struct xz_buf *b);
215 
216 /**
217  * xz_dec_reset() - Reset an already allocated decoder state
218  * @s:          Decoder state allocated using xz_dec_init()
219  *
220  * This function can be used to reset the multi-call decoder state without
221  * freeing and reallocating memory with xz_dec_end() and xz_dec_init().
222  *
223  * In single-call mode, xz_dec_reset() is always called in the beginning of
224  * xz_dec_run(). Thus, explicit call to xz_dec_reset() is useful only in
225  * multi-call mode.
226  */
227 XZ_EXTERN void xz_dec_reset(struct xz_dec *s);
228 
229 /**
230  * xz_dec_end() - Free the memory allocated for the decoder state
231  * @s:          Decoder state allocated using xz_dec_init(). If s is NULL,
232  *              this function does nothing.
233  */
234 XZ_EXTERN void xz_dec_end(struct xz_dec *s);
235 
236 /*
237  * Standalone build (userspace build or in-kernel build for boot time use)
238  * needs a CRC32 implementation. For normal in-kernel use, kernel's own
239  * CRC32 module is used instead, and users of this module don't need to
240  * care about the functions below.
241  */
242 #ifndef XZ_INTERNAL_CRC32
243 #	ifdef __KERNEL__
244 #		define XZ_INTERNAL_CRC32 0
245 #	else
246 #		define XZ_INTERNAL_CRC32 1
247 #	endif
248 #endif
249 
250 #if XZ_INTERNAL_CRC32
251 /*
252  * This must be called before any other xz_* function to initialize
253  * the CRC32 lookup table.
254  */
255 XZ_EXTERN void xz_crc32_init(void);
256 
257 /*
258  * Update CRC32 value using the polynomial from IEEE-802.3. To start a new
259  * calculation, the third argument must be zero. To continue the calculation,
260  * the previously returned value is passed as the third argument.
261  */
262 XZ_EXTERN uint32_t xz_crc32(const uint8_t *buf, size_t size, uint32_t crc);
263 #endif
264 #endif
265