[patch 30/47] exec: fix stack excutability without PT_GNU_STACK

Greg KH
2008-07-22T23:28:31Z

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2.6.25-stable review patch. If anyone has any objections, please let us
know.

------------------
From: Hugh Dickins <hugh@veritas.com>

commit 96a8e13ed44e380fc2bb6c711d74d5ba698c00b2 upstream

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@freemail.hu
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

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

--- a/fs/exec.c
+++ b/fs/exec.c
@@ -605,7 +605,7 @@ 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

--