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Linux/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 - '';
 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 
129                         if (nextoff)
130                                 *nextoff = (long)nptr - (long)data;
131 
132                         if (ch[C_NAMESIZE] - mypathsize >= MAX_CPIO_FILE_NAME) {
133                                 pr_warn(
134                                 "File %s exceeding MAX_CPIO_FILE_NAME [%d]\n",
135                                 p, MAX_CPIO_FILE_NAME);
136                         }
137                         strlcpy(cd.name, p + mypathsize, MAX_CPIO_FILE_NAME);
138 
139                         cd.data = (void *)dptr;
140                         cd.size = ch[C_FILESIZE];
141                         return cd; /* Found it! */
142                 }
143                 len -= (nptr - p);
144                 p = nptr;
145         }
146 
147 quit:
148         return cd;
149 }
150 

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