lib/earlycpio.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* ----------------------------------------------------------------------- *
   3  *
   4  *   Copyright 2012 Intel Corporation; author H. Peter Anvin
   5  *
   6  * ----------------------------------------------------------------------- */
   7
   8 /*
   9  * earlycpio.c
  10  *
  11  * Find a specific cpio member; must precede any compressed content.
  12  * This is used to locate data items in the initramfs used by the
  13  * kernel itself during early boot (before the main initramfs is
  14  * decompressed.)  It is the responsibility of the initramfs creator
  15  * to ensure that these items are uncompressed at the head of the
  16  * blob.  Depending on the boot loader or package tool that may be a
  17  * separate file or part of the same file.
  18  */
  19
  20 #include <linux/earlycpio.h>
  21 #include <linux/kernel.h>
  22 #include <linux/string.h>
  23
  24 enum cpio_fields {
  25         C_MAGIC,
  26         C_INO,
  27         C_MODE,
  28         C_UID,
  29         C_GID,
  30         C_NLINK,
  31         C_MTIME,
  32         C_FILESIZE,
  33         C_MAJ,
  34         C_MIN,
  35         C_RMAJ,
  36         C_RMIN,
  37         C_NAMESIZE,
  38         C_CHKSUM,
  39         C_NFIELDS
  40 };
  41
  42 /**
  43  * cpio_data find_cpio_data - Search for files in an uncompressed cpio
  44  * @path:       The directory to search for, including a slash at the end
  45  * @data:       Pointer to the cpio archive or a header inside
  46  * @len:        Remaining length of the cpio based on data pointer
  47  * @nextoff:    When a matching file is found, this is the offset from the
  48  *              beginning of the cpio to the beginning of the next file, not the
  49  *              matching file itself. It can be used to iterate through the cpio
  50  *              to find all files inside of a directory path.
  51  *
  52  * @return:     struct cpio_data containing the address, length and
  53  *              filename (with the directory path cut off) of the found file.
  54  *              If you search for a filename and not for files in a directory,
  55  *              pass the absolute path of the filename in the cpio and make sure
  56  *              the match returned an empty filename string.
  57  */
  58
  59 struct cpio_data find_cpio_data(const char *path, void *data,
  60                                 size_t len,  long *nextoff)
  61 {
  62         const size_t cpio_header_len = 8*C_NFIELDS - 2;
  63         struct cpio_data cd = { NULL, 0, "" };
  64         const char *p, *dptr, *nptr;
  65         unsigned int ch[C_NFIELDS], *chp, v;
  66         unsigned char c, x;
  67         size_t mypathsize = strlen(path);
  68         int i, j;
  69
  70         p = data;
  71
  72         while (len > cpio_header_len) {
  73                 if (!*p) {
  74                         /* All cpio headers need to be 4-byte aligned */
  75                         p += 4;
  76                         len -= 4;
  77                         continue;
  78                 }
  79
  80                 j = 6;          /* The magic field is only 6 characters */
  81                 chp = ch;
  82                 for (i = C_NFIELDS; i; i--) {
  83                         v = 0;
  84                         while (j--) {
  85                                 v <<= 4;
  86                                 c = *p++;
  87
  88                                 x = c - '0';
  89                                 if (x < 10) {
  90                                         v += x;
  91                                         continue;
  92                                 }
  93
  94                                 x = (c | 0x20) - 'a';
  95                                 if (x < 6) {
  96                                         v += x + 10;
  97                                         continue;
  98                                 }
  99
 100                                 goto quit; /* Invalid hexadecimal */
 101                         }
 102                         *chp++ = v;
 103                         j = 8;  /* All other fields are 8 characters */
 104                 }
 105
 106                 if ((ch[C_MAGIC] - 0x070701) > 1)
 107                         goto quit; /* Invalid magic */
 108
 109                 len -= cpio_header_len;
 110
 111                 dptr = PTR_ALIGN(p + ch[C_NAMESIZE], 4);
 112                 nptr = PTR_ALIGN(dptr + ch[C_FILESIZE], 4);
 113
 114                 if (nptr > p + len || dptr < p || nptr < dptr)
 115                         goto quit; /* Buffer overrun */
 116
 117                 if ((ch[C_MODE] & 0170000) == 0100000 &&
 118                     ch[C_NAMESIZE] >= mypathsize &&
 119                     !memcmp(p, path, mypathsize)) {
 120
 121                         if (nextoff)
 122                                 *nextoff = (long)nptr - (long)data;
 123
 124                         if (ch[C_NAMESIZE] - mypathsize >= MAX_CPIO_FILE_NAME) {
 125                                 pr_warn(
 126                                 "File %s exceeding MAX_CPIO_FILE_NAME [%d]\n",
 127                                 p, MAX_CPIO_FILE_NAME);
 128                         }
 129                         strlcpy(cd.name, p + mypathsize, MAX_CPIO_FILE_NAME);
 130
 131                         cd.data = (void *)dptr;
 132                         cd.size = ch[C_FILESIZE];
 133                         return cd; /* Found it! */
 134                 }
 135                 len -= (nptr - p);
 136                 p = nptr;
 137         }
 138
 139 quit:
 140         return cd;
 141 }