Root/lib/earlycpio.c

1/* ----------------------------------------------------------------------- *
2 *
3 * Copyright 2012 Intel Corporation; author H. Peter Anvin
4 *
5 * This file is part of the Linux kernel, and is made available
6 * under the terms of the GNU General Public License version 2, as
7 * published by the Free Software Foundation.
8 *
9 * This program is distributed in the hope it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
13 *
14 * ----------------------------------------------------------------------- */
15
16/*
17 * earlycpio.c
18 *
19 * Find a specific cpio member; must precede any compressed content.
20 * This is used to locate data items in the initramfs used by the
21 * kernel itself during early boot (before the main initramfs is
22 * decompressed.) It is the responsibility of the initramfs creator
23 * to ensure that these items are uncompressed at the head of the
24 * blob. Depending on the boot loader or package tool that may be a
25 * separate file or part of the same file.
26 */
27
28#include <linux/earlycpio.h>
29#include <linux/kernel.h>
30#include <linux/string.h>
31
32enum cpio_fields {
33    C_MAGIC,
34    C_INO,
35    C_MODE,
36    C_UID,
37    C_GID,
38    C_NLINK,
39    C_MTIME,
40    C_FILESIZE,
41    C_MAJ,
42    C_MIN,
43    C_RMAJ,
44    C_RMIN,
45    C_NAMESIZE,
46    C_CHKSUM,
47    C_NFIELDS
48};
49
50/**
51 * cpio_data find_cpio_data - Search for files in an uncompressed cpio
52 * @path: The directory to search for, including a slash at the end
53 * @data: Pointer to the the cpio archive or a header inside
54 * @len: Remaining length of the cpio based on data pointer
55 * @nextoff: When a matching file is found, this is the offset from the
56 * beginning of the cpio to the beginning of the next file, not the
57 * matching file itself. It can be used to iterate through the cpio
58 * to find all files inside of a directory path.
59 *
60 * @return: struct cpio_data containing the address, length and
61 * filename (with the directory path cut off) of the found file.
62 * If you search for a filename and not for files in a directory,
63 * pass the absolute path of the filename in the cpio and make sure
64 * the match returned an empty filename string.
65 */
66
67struct cpio_data find_cpio_data(const char *path, void *data,
68                size_t len, long *nextoff)
69{
70    const size_t cpio_header_len = 8*C_NFIELDS - 2;
71    struct cpio_data cd = { NULL, 0, "" };
72    const char *p, *dptr, *nptr;
73    unsigned int ch[C_NFIELDS], *chp, v;
74    unsigned char c, x;
75    size_t mypathsize = strlen(path);
76    int i, j;
77
78    p = data;
79
80    while (len > cpio_header_len) {
81        if (!*p) {
82            /* All cpio headers need to be 4-byte aligned */
83            p += 4;
84            len -= 4;
85            continue;
86        }
87
88        j = 6; /* The magic field is only 6 characters */
89        chp = ch;
90        for (i = C_NFIELDS; i; i--) {
91            v = 0;
92            while (j--) {
93                v <<= 4;
94                c = *p++;
95
96                x = c - '0';
97                if (x < 10) {
98                    v += x;
99                    continue;
100                }
101
102                x = (c | 0x20) - 'a';
103                if (x < 6) {
104                    v += x + 10;
105                    continue;
106                }
107
108                goto quit; /* Invalid hexadecimal */
109            }
110            *chp++ = v;
111            j = 8; /* All other fields are 8 characters */
112        }
113
114        if ((ch[C_MAGIC] - 0x070701) > 1)
115            goto quit; /* Invalid magic */
116
117        len -= cpio_header_len;
118
119        dptr = PTR_ALIGN(p + ch[C_NAMESIZE], 4);
120        nptr = PTR_ALIGN(dptr + ch[C_FILESIZE], 4);
121
122        if (nptr > p + len || dptr < p || nptr < dptr)
123            goto quit; /* Buffer overrun */
124
125        if ((ch[C_MODE] & 0170000) == 0100000 &&
126            ch[C_NAMESIZE] >= mypathsize &&
127            !memcmp(p, path, mypathsize)) {
128            *nextoff = (long)nptr - (long)data;
129            if (ch[C_NAMESIZE] - mypathsize >= MAX_CPIO_FILE_NAME) {
130                pr_warn(
131                "File %s exceeding MAX_CPIO_FILE_NAME [%d]\n",
132                p, MAX_CPIO_FILE_NAME);
133            }
134            strlcpy(cd.name, p + mypathsize, MAX_CPIO_FILE_NAME);
135
136            cd.data = (void *)dptr;
137            cd.size = ch[C_FILESIZE];
138            return cd; /* Found it! */
139        }
140        len -= (nptr - p);
141        p = nptr;
142    }
143
144quit:
145    return cd;
146}
147

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