Fix check for bad address; use macro instead of open-coding two checks.

Taken from RHEL4 kernel update.

From: Ernie Petrides <petrides@redhat.com>

  For background, the BAD_ADDR() macro should return TRUE if the address is
  TASK_SIZE, because that's the lowest address that is *not* valid for
  user-space mappings.  The macro was correct in binfmt_aout.c but was wrong
  for the "equal to" case in binfmt_elf.c.  There were two in-line validations
  of user-space addresses in binfmt_elf.c, which have been appropriately
  converted to use the corrected BAD_ADDR() macro in the patch you posted
  yesterday.  Note that the size checks against TASK_SIZE are okay as coded.

  The additional changes that I propose are below.  These are in the error
  paths for bad ELF entry addresses once load_elf_binary() has already
  committed to exec'ing the new image (following the tearing down of the
  task's original address space).

  The 1st hunk deals with the interp-side of the outer "if".  There were two
  problems here.  The printk() should be removed because this path can be
  triggered at will by a bogus interpreter image created and used by a
  malicious user.  Further, the error code should not be ENOEXEC, because that
  causes the loop in search_binary_handler() to continue trying other exec
  handlers (twice, in fact).  But it's too late for this to work correctly,
  because the user address space has already been torn down, and an exec()
  failure cannot be returned to the user code because the code no longer
  exists.  The only recovery is to force a SIGSEGV, but it's best to terminate
  the search loop immediately.  I somewhat arbitrarily chose EINVAL as a
  fallback error code, but any error returned by load_elf_interp() will
  override that (but this value will never be seen by user-space).

  The 2nd hunk deals with the non-interp-side of the outer "if".  There were
  two problems here as well.  The SIGSEGV needs to be forced, because a prior
  sigaction() syscall might have set the associated disposition to SIG_IGN.
  And the ENOEXEC should be changed to EINVAL as described above.
Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Ernie Petrides <petrides@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>