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
  32 enum 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
  66 struct 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
 143 quit:
 144         return cd;
 145 }