1 /* Copyright 2014 The ChromiumOS Authors
2 * Use of this source code is governed by a BSD-style license that can be
3 * found in the LICENSE file.
4 */
5
6 #include <elf.h>
7 #include <endian.h>
8 #include <stdint.h>
9 #include <stdio.h>
10 #include <stdlib.h>
11 #include <unistd.h>
12
13 #include "elfparse.h"
14 #include "util.h"
15
is_elf_magic(const uint8_t * buf)16 int is_elf_magic (const uint8_t *buf)
17 {
18 return (buf[EI_MAG0] == ELFMAG0) &&
19 (buf[EI_MAG1] == ELFMAG1) &&
20 (buf[EI_MAG2] == ELFMAG2) &&
21 (buf[EI_MAG3] == ELFMAG3);
22 }
23
24 #define parseElftemplate(bit) \
25 ElfType parseElf ## bit(FILE *elf_file, uint8_t *pHead, int little_endian) \
26 { \
27 ElfType ret = ELFSTATIC; \
28 Minijail_Elf ## bit ## _Ehdr *pHeader = NULL; \
29 Minijail_Elf ## bit ## _Phdr pheader; \
30 uint32_t i = 0; \
31 \
32 if (!elf_file || !pHead) \
33 return ELFERROR; \
34 \
35 pHeader = (Minijail_Elf ## bit ## _Ehdr *)pHead; \
36 if (little_endian) { \
37 pHeader->e_phoff = le ## bit ## toh(pHeader->e_phoff); \
38 pHeader->e_phentsize = le16toh(pHeader->e_phentsize); \
39 pHeader->e_phnum = le16toh(pHeader->e_phnum); \
40 } else { \
41 pHeader->e_phoff = be ## bit ## toh(pHeader->e_phoff); \
42 pHeader->e_phentsize = be16toh(pHeader->e_phentsize); \
43 pHeader->e_phnum = be16toh(pHeader->e_phnum); \
44 } \
45 if (pHeader->e_phentsize != sizeof(Minijail_Elf ## bit ## _Phdr)) \
46 return ELFERROR; \
47 \
48 if (fseek(elf_file, pHeader->e_phoff, SEEK_SET) != 0) \
49 return ELFERROR; \
50 \
51 for (i = 0; i < pHeader->e_phnum; i++) { \
52 if (fread(&pheader, sizeof(pheader), 1, elf_file) == 1) { \
53 if (pheader.p_type == PT_INTERP) { \
54 ret = ELFDYNAMIC; \
55 break; \
56 } \
57 } else { \
58 ret = ELFERROR; \
59 break; \
60 } \
61 } \
62 return ret; \
63 }
64 parseElftemplate(64)
65 parseElftemplate(32)
66
67 /* Public function to determine the linkage of an ELF. */
get_elf_linkage(const char * path)68 ElfType get_elf_linkage(const char *path)
69 {
70 ElfType ret = ELFERROR;
71 attribute_cleanup_fp FILE *elf_file = NULL;
72 uint8_t pHeader[HEADERSIZE] = "";
73
74 elf_file = fopen(path, "re");
75 if (elf_file) {
76 if (fread(pHeader, 1, HEADERSIZE, elf_file) == HEADERSIZE) {
77 if (is_elf_magic(pHeader)) {
78 if ((pHeader[EI_DATA] == ELFDATA2LSB) &&
79 (pHeader[EI_CLASS] == ELFCLASS64)) {
80 /* 64-bit little endian. */
81 ret = parseElf64(elf_file, pHeader, 1);
82 } else if ((pHeader[EI_DATA] == ELFDATA2MSB) &&
83 (pHeader[EI_CLASS] == ELFCLASS64)) {
84 /* 64-bit big endian. */
85 ret = parseElf64(elf_file, pHeader, 0);
86 } else if ((pHeader[EI_DATA] == ELFDATA2LSB) &&
87 (pHeader[EI_CLASS] == ELFCLASS32)) {
88 /* 32-bit little endian. */
89 ret = parseElf32(elf_file, pHeader, 1);
90 } else if ((pHeader[EI_DATA] == ELFDATA2MSB) &&
91 (pHeader[EI_CLASS] == ELFCLASS32)) {
92 /* 32-bit big endian. */
93 ret = parseElf32(elf_file, pHeader, 0);
94 }
95 } else {
96 /*
97 * The binary is not an ELF. We assume it's a
98 * script. We should parse the #! line and
99 * check the interpreter to guard against
100 * static interpreters escaping the sandbox.
101 * As Minijail is only called from the rootfs
102 * it was deemed not necessary to check this.
103 * So we will just let execve(2) decide if this
104 * is valid.
105 */
106 ret = ELFDYNAMIC;
107 }
108 } else {
109 /*
110 * The file is smaller than |HEADERSIZE| bytes.
111 * We assume it's a short script. See above for
112 * reasoning on scripts.
113 */
114 ret = ELFDYNAMIC;
115 }
116 }
117 return ret;
118 }
119