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  * 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 
find_cpio_data(const char * path,void * data,size_t len,long * nextoff)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 			strscpy(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 }
142