linux-kernel - [Bug 11063][PATCH] exec: fix stack excutability without PT_GNU

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Date:	Thu, 10 Jul 2008 21:19:20 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ollie Wild <aaw@...gle.com>, bugme-daemon@...zilla.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Roland McGrath <roland@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, pageexec@...email.hu,
	stable@...nel.org, linux-kernel@...r.kernel.org
Subject: [Bug 11063][PATCH] exec: fix stack excutability without PT_GNU_STACK

Kernel Bugzilla #11063 points out that on some architectures (e.g. x86_32)
exec'ing an ELF without a PT_GNU_STACK program header should default to an
executable stack; but this got broken by the unlimited argv feature because
stack vma is now created before the right personality has been established:
so breaking old binaries using nested function trampolines.

Therefore re-evaluate VM_STACK_FLAGS in setup_arg_pages, where stack
vm_flags used to be set, before the mprotect_fixup.  Checking through
our existing VM_flags, none would have changed since insert_vm_struct:
so this seems safer than finding a way through the personality labyrinth.

Reported-by: pageexec@...email.hu
Signed-off-by: Hugh Dickins <hugh@...itas.com>
Cc: stable@...nel.org
---

 fs/exec.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 2.6.26-rc9/fs/exec.c	2008-06-21 08:41:19.000000000 +0100
+++ linux/fs/exec.c	2008-07-10 20:02:25.000000000 +0100
@@ -610,7 +610,7 @@ int setup_arg_pages(struct linux_binprm 
 	bprm->exec -= stack_shift;

 	down_write(&mm->mmap_sem);
-	vm_flags = vma->vm_flags;
+	vm_flags = VM_STACK_FLAGS;

 	/*
 	 * Adjust stack execute permissions; explicitly enable for
--
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