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#include <dlfcn.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#ifndef LINKER
#error LINKER must be defined
#endif
static char exe[PATH_MAX], *linker;
static ssize_t (*real_readlink)(const char *, char *, size_t);
ssize_t readlink(const char *path, char *buf, size_t len)
{
if (real_readlink == NULL) {
real_readlink = dlsym(RTLD_NEXT, "readlink");
if (real_readlink == NULL) {
errno = ENOSYS;
return -1;
}
}
if (!strcmp(path, "/proc/self/exe")) {
int fd;
if (exe[0] == '\0') {
if (linker == NULL) {
linker = realpath(LINKER, NULL);
if (linker == NULL) {
return -1;
}
}
if (real_readlink(path, exe, sizeof(exe)) < 1) {
goto fail;
}
if (!strcmp(exe, linker)) {
char c;
int arg = 0;
ssize_t arglen;
fd = open("/proc/self/cmdline",
O_RDONLY | O_CLOEXEC);
if (fd < 0) {
goto fail;
}
/* Skip the --argv0/--preload ldso args.
* This number must be kept in sync with the
* argument order in loader/loader.c */
while (arg < 5) {
if (read(fd, &c, 1) != 1) {
goto fail_close;
}
if (c == '\0') {
++arg;
}
}
/* Read the executable path from the cmdline. */
arglen = read(fd, exe, sizeof(exe));
if (arglen < 1) {
goto fail_close;
}
close(fd);
/* Ensure the path exists, fits, and has NUL. */
if (exe[0] == '\0') {
goto fail;
}
if (strnlen(exe, arglen) == (size_t) arglen) {
goto fail;
}
}
}
return stpncpy(buf, exe, len) - buf;
fail_close:
close(fd);
fail:
exe[0] = '\0';
return -1;
}
return real_readlink(path, buf, len);
}
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