[PATCH] binfmt_elf bss padding fix

Nir Tzachar <tzachar@cs.bgu.ac.il> points out that if an ELF file specifies a
zero-length bss at a whacky address, we cannot load that binary because
padzero() tries to zero out the end of the page at the whacky address, and
that may not be writeable.

See also http://bugzilla.kernel.org/show_bug.cgi?id=5411

So teach load_elf_binary() to skip the bss settng altogether if the elf file
has a zero-length bss segment.

Cc: Roland McGrath <roland@redhat.com>
Cc: Daniel Jacobowitz <dan@debian.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/binfmt_elf.c

@@ -905,7 +905,7 @@ static int load_elf_binary(struct linux_binprm * bprm, struct pt_regs * regs)
 		send_sig(SIGKILL, current, 0);
 		goto out_free_dentry;
 	}
-	if (padzero(elf_bss)) {
+	if (likely(elf_bss != elf_brk) && unlikely(padzero(elf_bss))) {
 		send_sig(SIGSEGV, current, 0);
 		retval = -EFAULT; /* Nobody gets to see this, but.. */
 		goto out_free_dentry;