linux/lib/earlycpio.c
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   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 * @offset: When a matching file is found, this is the offset to the
  56 *          beginning of the cpio. It can be used to iterate through
  57 *          the cpio to find all files inside of a directory path
  58 *
  59 * @return: struct cpio_data containing the address, length and
  60 *          filename (with the directory path cut off) of the found file.
  61 *          If you search for a filename and not for files in a directory,
  62 *          pass the absolute path of the filename in the cpio and make sure
  63 *          the match returned an empty filename string.
  64 */
  65
  66struct cpio_data __cpuinit find_cpio_data(const char *path, void *data,
  67                                          size_t len,  long *offset)
  68{
  69        const size_t cpio_header_len = 8*C_NFIELDS - 2;
  70        struct cpio_data cd = { NULL, 0, "" };
  71        const char *p, *dptr, *nptr;
  72        unsigned int ch[C_NFIELDS], *chp, v;
  73        unsigned char c, x;
  74        size_t mypathsize = strlen(path);
  75        int i, j;
  76
  77        p = data;
  78
  79        while (len > cpio_header_len) {
  80                if (!*p) {
  81                        /* All cpio headers need to be 4-byte aligned */
  82                        p += 4;
  83                        len -= 4;
  84                        continue;
  85                }
  86
  87                j = 6;          /* The magic field is only 6 characters */
  88                chp = ch;
  89                for (i = C_NFIELDS; i; i--) {
  90                        v = 0;
  91                        while (j--) {
  92                                v <<= 4;
  93                                c = *p++;
  94
  95                                x = c - '0';
  96                                if (x < 10) {
  97                                        v += x;
  98                                        continue;
  99                                }
 100
 101                                x = (c | 0x20) - 'a';
 102                                if (x < 6) {
 103                                        v += x + 10;
 104                                        continue;
 105                                }
 106
 107                                goto quit; /* Invalid hexadecimal */
 108                        }
 109                        *chp++ = v;
 110                        j = 8;  /* All other fields are 8 characters */
 111                }
 112
 113                if ((ch[C_MAGIC] - 0x070701) > 1)
 114                        goto quit; /* Invalid magic */
 115
 116                len -= cpio_header_len;
 117
 118                dptr = PTR_ALIGN(p + ch[C_NAMESIZE], 4);
 119                nptr = PTR_ALIGN(dptr + ch[C_FILESIZE], 4);
 120
 121                if (nptr > p + len || dptr < p || nptr < dptr)
 122                        goto quit; /* Buffer overrun */
 123
 124                if ((ch[C_MODE] & 0170000) == 0100000 &&
 125                    ch[C_NAMESIZE] >= mypathsize &&
 126                    !memcmp(p, path, mypathsize)) {
 127                        *offset = (long)nptr - (long)data;
 128                        if (ch[C_NAMESIZE] - mypathsize >= MAX_CPIO_FILE_NAME) {
 129                                pr_warn(
 130                                "File %s exceeding MAX_CPIO_FILE_NAME [%d]\n",
 131                                p, MAX_CPIO_FILE_NAME);
 132                        }
 133                        strlcpy(cd.name, p + mypathsize, MAX_CPIO_FILE_NAME);
 134
 135                        cd.data = (void *)dptr;
 136                        cd.size = ch[C_FILESIZE];
 137                        return cd; /* Found it! */
 138                }
 139                len -= (nptr - p);
 140                p = nptr;
 141        }
 142
 143quit:
 144        return cd;
 145}
 146
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