earlycpio.c
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// SPDX-License-Identifier: GPL-2.0-only
/* ----------------------------------------------------------------------- *
*
* Copyright 2012 Intel Corporation; author H. Peter Anvin
*
* ----------------------------------------------------------------------- */
/*
* earlycpio.c
*
* Find a specific cpio member; must precede any compressed content.
* This is used to locate data items in the initramfs used by the
* kernel itself during early boot (before the main initramfs is
* decompressed.) It is the responsibility of the initramfs creator
* to ensure that these items are uncompressed at the head of the
* blob. Depending on the boot loader or package tool that may be a
* separate file or part of the same file.
*/
#include <linux/earlycpio.h>
#include <linux/kernel.h>
#include <linux/string.h>
enum cpio_fields {
C_MAGIC,
C_INO,
C_MODE,
C_UID,
C_GID,
C_NLINK,
C_MTIME,
C_FILESIZE,
C_MAJ,
C_MIN,
C_RMAJ,
C_RMIN,
C_NAMESIZE,
C_CHKSUM,
C_NFIELDS
};
/**
* cpio_data find_cpio_data - Search for files in an uncompressed cpio
* @path: The directory to search for, including a slash at the end
* @data: Pointer to the the cpio archive or a header inside
* @len: Remaining length of the cpio based on data pointer
* @nextoff: When a matching file is found, this is the offset from the
* beginning of the cpio to the beginning of the next file, not the
* matching file itself. It can be used to iterate through the cpio
* to find all files inside of a directory path.
*
* @return: struct cpio_data containing the address, length and
* filename (with the directory path cut off) of the found file.
* If you search for a filename and not for files in a directory,
* pass the absolute path of the filename in the cpio and make sure
* the match returned an empty filename string.
*/
struct cpio_data find_cpio_data(const char *path, void *data,
size_t len, long *nextoff)
{
const size_t cpio_header_len = 8*C_NFIELDS - 2;
struct cpio_data cd = { NULL, 0, "" };
const char *p, *dptr, *nptr;
unsigned int ch[C_NFIELDS], *chp, v;
unsigned char c, x;
size_t mypathsize = strlen(path);
int i, j;
p = data;
while (len > cpio_header_len) {
if (!*p) {
/* All cpio headers need to be 4-byte aligned */
p += 4;
len -= 4;
continue;
}
j = 6; /* The magic field is only 6 characters */
chp = ch;
for (i = C_NFIELDS; i; i--) {
v = 0;
while (j--) {
v <<= 4;
c = *p++;
x = c - '0';
if (x < 10) {
v += x;
continue;
}
x = (c | 0x20) - 'a';
if (x < 6) {
v += x + 10;
continue;
}
goto quit; /* Invalid hexadecimal */
}
*chp++ = v;
j = 8; /* All other fields are 8 characters */
}
if ((ch[C_MAGIC] - 0x070701) > 1)
goto quit; /* Invalid magic */
len -= cpio_header_len;
dptr = PTR_ALIGN(p + ch[C_NAMESIZE], 4);
nptr = PTR_ALIGN(dptr + ch[C_FILESIZE], 4);
if (nptr > p + len || dptr < p || nptr < dptr)
goto quit; /* Buffer overrun */
if ((ch[C_MODE] & 0170000) == 0100000 &&
ch[C_NAMESIZE] >= mypathsize &&
!memcmp(p, path, mypathsize)) {
if (nextoff)
*nextoff = (long)nptr - (long)data;
if (ch[C_NAMESIZE] - mypathsize >= MAX_CPIO_FILE_NAME) {
pr_warn(
"File %s exceeding MAX_CPIO_FILE_NAME [%d]\n",
p, MAX_CPIO_FILE_NAME);
}
strlcpy(cd.name, p + mypathsize, MAX_CPIO_FILE_NAME);
cd.data = (void *)dptr;
cd.size = ch[C_FILESIZE];
return cd; /* Found it! */
}
len -= (nptr - p);
p = nptr;
}
quit:
return cd;
}