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  * @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
  67 struct 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
 144 quit:
 145         return cd;
 146 }