1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
|
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <dirent.h>
#include <assert.h>
#include <string.h>
#include <errno.h>
/* Make sure assertions are not compiled out. */
#undef NDEBUG
extern char **environ;
static char * wrapperDir = WRAPPER_DIR;
int main(int argc, char * * argv)
{
char self[PATH_MAX];
int len = readlink("/proc/self/exe", self, sizeof(self) - 1);
assert (len > 0);
self[len] = 0;
/* Make sure that we are being executed from the right location,
i.e., `wrapperDir'. This is to prevent someone from
creating hard link `X' from some other location, along with a
false `X.real' file, to allow arbitrary programs from being
executed setuid. */
assert ((strncmp(self, wrapperDir, strlen(wrapperDir)) == 0) &&
(self[strlen(wrapperDir)] == '/'));
/* Make *really* *really* sure that we were executed as `self',
and not, say, as some other setuid program. That is, our
effective uid/gid should match the uid/gid of `self'. */
//printf("%d %d\n", geteuid(), getegid());
struct stat st;
assert (lstat(self, &st) != -1);
//printf("%d %d\n", st.st_uid, st.st_gid);
assert ((st.st_mode & S_ISUID) == 0 ||
(st.st_uid == geteuid()));
assert ((st.st_mode & S_ISGID) == 0 ||
st.st_gid == getegid());
/* And, of course, we shouldn't be writable. */
assert (!(st.st_mode & (S_IWGRP | S_IWOTH)));
/* Read the path of the real (wrapped) program from <self>.real. */
char realFN[PATH_MAX + 10];
int realFNSize = snprintf (realFN, sizeof(realFN), "%s.real", self);
assert (realFNSize < sizeof(realFN));
int fdSelf = open(realFN, O_RDONLY);
assert (fdSelf != -1);
char real[PATH_MAX];
len = read(fdSelf, real, PATH_MAX);
assert (len != -1);
assert (len < sizeof (real));
assert (len > 0);
real[len] = 0;
close(fdSelf);
//printf("real = %s, len = %d\n", real, len);
execve(real, argv, environ);
fprintf(stderr, "%s: cannot run `%s': %s\n",
argv[0], real, strerror(errno));
exit(1);
}
|