linux-kernel - [Patch] Elf loader crash while zero-filling .bss

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Message-ID: <15577be70802111027s59bc16f7q7c0be42cc44f9ad7@mail.gmail.com>
Date:	Mon, 11 Feb 2008 19:27:35 +0100
From:	"Abel Bernabeu" <abelbg@...rp.com>
To:	linux-kernel@...r.kernel.org
Subject: [Patch] Elf loader crash while zero-filling .bss

I've finally found a solution for the crash in load_binary_elf I
reported last week:

http://lkml.org/lkml/2008/1/30/171

The attached patch solves my problem, but please test it yourself...

set_brk(start, end) allocs just page aligned regions (by "colapsing"
both extremes to the start of the page in which they lay)... That
means than even if both pointers are not equal there are still some
chances that set_brk has allocated no space at all because
ELF_PAGEALIGN(elf_bss) != ELF_PAGEALIGN(elf_brk).

So the condition was not correct.

--- linux-2.6.22.10.orig/fs/binfmt_elf.c	2008-02-11 18:58:29.000000000 +0100
+++ linux-2.6.22.10.hacked/fs/binfmt_elf.c	2008-02-11 16:09:41.000000000 +0100
@@ -939,3 +939,3 @@ static int load_elf_binary(struct linux_
 	}
-	if (likely(elf_bss != elf_brk) && unlikely(padzero(elf_bss))) {
+	if (likely(ELF_PAGEALIGN(elf_bss) != ELF_PAGEALIGN(elf_brk)) &&
unlikely(padzero(elf_bss))) {
 		send_sig(SIGSEGV, current, 0);
--
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