linux-kernel - Re: Is it legal to return positive value when do

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Date:	Tue,  5 Oct 2010 11:55:06 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Is it legal to return positive value when do_execve() succeeds?

> > > KOSAKI Motohiro wrote:
> > > > > fs/binfmt_elf.c:
> > > > >  77 #define BAD_ADDR(x) ((unsigned long)(x) >= TASK_SIZE)
> > > > Can do_brk() return BAD_ADDR() _and_ !IS_ERR_VALUE() value? when?
> > > 
> > > For example, arch/mips/include/asm/processor.h has below definitions
> > > which is smaller than INT_MAX
> > > 
> > >  47 #ifdef CONFIG_32BIT
> > > (...snipped...)
> > >  52 #define TASK_SIZE       0x7fff8000UL
> > > (...snipped...)
> > >  63 #endif
> > >  64 
> > >  65 #ifdef CONFIG_64BIT
> > > (...snipped...)
> > >  74 #define TASK_SIZE       0x10000000000UL
> > > (...snipped...)
> > >  91 #endif
> > > 
> > > Also, several architectures define TASK_SIZE as
> > > 
> > >   #define TASK_SIZE               PAGE_OFFSET
> > > 
> > > and PAGE_OFFSET could be 0 if CONFIG_KERNEL_RAM_BASE_ADDRESS is not defined.
> > > 
> > > include/asm-generic/page.h
> > >  68 #ifdef CONFIG_KERNEL_RAM_BASE_ADDRESS
> > >  69 #define PAGE_OFFSET             (CONFIG_KERNEL_RAM_BASE_ADDRESS)
> > >  70 #else
> > >  71 #define PAGE_OFFSET             (0)
> > >  72 #endif
> > > 
> > > If TASK_SIZE == 0, BAD_ADDR(x) is always true and !IS_ERR_VALUE(x) can be true.
> > > Although I don't know which combination makes such environment,
> > > I think "BAD_ADDR() _and_ !IS_ERR_VALUE()" can happen.
> > 
> > I think you should read do_brk() itself. the spec is
> > 
> > success case:
> > 	return addr argument
> > 
> > error case: 
> > 	return error code
> > 
> > When does it return invalid address?
> 
> Does this makes a bit cleanups?
> 
> 
> 
> From 5f5556d30ac1876ec2211a2eae77e8372183a9b1 Mon Sep 17 00:00:00 2001
> From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Date: Fri, 15 Oct 2010 05:13:40 +0900
> Subject: [cleanup][PATCH] elf: kill BAD_ADDR() macro
> 
> BAD_ADDR() macro is useless because 1) do_brk() and do_mmap() return
> only either valid pointer or error code 2) when kernel and userland have
> perfectly different address space (such as old 4G:4G separation), to
> compare TASK_SIZE has no good meaning.
> 
> Then, this patch change it to use IS_ERR_VALUE instead (as other a lot
> of places).
> But, this is theorical issue. this patch doesn't have functional change.

Ouch, this patch is completely corrupted. please ignore it.



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