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/*
* This program manages user stack area executability flag for ELF and a.out
* binaries. The flag only has effect when running the patched Linux kernel.
*
* Written by Solar Designer and placed in the public domain.
*/
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/elf.h>
#include <linux/a.out.h>
#define HF_STACKEXEC 1
static struct elf32_hdr header_elf;
static struct exec header_aout;
static void *header;
static int header_size;
static int fd;
static unsigned long (*get_flags)();
static void (*put_flags)(unsigned long);
static unsigned long get_flags_elf()
{
return header_elf.e_flags;
}
static void put_flags_elf(unsigned long flags)
{
header_elf.e_flags = flags;
}
static unsigned long get_flags_aout()
{
return N_FLAGS(header_aout);
}
static void put_flags_aout(unsigned long flags)
{
N_SET_FLAGS(header_aout, flags);
}
static int read_header(char *name, int mode)
{
char *ptr;
int size, block;
if ((fd = open(name, mode)) < 0) return 1;
ptr = (char *)&header_elf;
size = sizeof(header_elf);
do {
block = read(fd, ptr, size);
if (block <= 0) {
close(fd);
return block ? 1 : 2;
}
ptr += block; size -= block;
} while (size > 0);
memcpy(&header_aout, &header_elf, sizeof(header_aout));
if (!strncmp(header_elf.e_ident, ELFMAG, SELFMAG)) {
if (header_elf.e_type != ET_EXEC) return 2;
if (header_elf.e_machine != EM_386) return 3;
header = &header_elf; header_size = sizeof(header_elf);
get_flags = get_flags_elf; put_flags = put_flags_elf;
} else
if (N_MAGIC(header_aout) == NMAGIC ||
N_MAGIC(header_aout) == ZMAGIC ||
N_MAGIC(header_aout) == QMAGIC) {
if (N_MACHTYPE(header_aout) != M_386) return 3;
header = &header_aout; header_size = 4;
get_flags = get_flags_aout; put_flags = put_flags_aout;
} else return 2;
return 0;
}
int write_header()
{
char *ptr;
int size, block;
if (lseek(fd, 0, SEEK_SET)) return 1;
ptr = (char *)header;
size = header_size;
do {
block = write(fd, ptr, size);
if (block <= 0) break;
ptr += block; size -= block;
} while (size > 0);
return size;
}
#define USAGE \
"Usage: %s OPTION FILE...\n" \
"Manage stack area executability flag for binaries\n\n" \
" -e\tenable execution permission\n" \
" -d\tdisable execution permission\n" \
" -v\tview current flag state\n\n" \
"The flag only has effect when running the patched Linux kernel\n"
void usage(char *name)
{
printf(USAGE, name ? name : "chstk");
exit(1);
}
int main(int argc, char **argv)
{
char **current;
unsigned long flags;
int error = 0;
int mode;
if (argc < 3) usage(argv[0]);
if (strlen(argv[1]) != 2) usage(argv[0]);
if (argv[1][0] != '-' || !strchr("edv", argv[1][1])) usage(argv[0]);
current = &argv[2];
do {
mode = argv[1][1] == 'v' ? O_RDONLY : O_RDWR;
switch (read_header(*current, mode)) {
case 1:
perror(*current);
error = 1; continue;
case 2:
printf("%s: Unknown file type\n", *current);
error = 1; continue;
case 3:
printf("%s: Wrong architecture\n", *current);
error = 1; continue;
}
flags = get_flags();
switch (argv[1][1]) {
case 'e':
put_flags(flags | HF_STACKEXEC);
break;
case 'd':
put_flags(flags & ~HF_STACKEXEC);
break;
default:
printf("%s: %s stack area\n", *current,
flags & HF_STACKEXEC
? "Executable" : "Non-executable");
}
if (flags != get_flags())
if (write_header()) {
perror(*current);
error = 1;
}
close(fd);
} while (*++current);
return error;
}
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