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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Subject: Re: Is it legal to return positive value when do_execve() succeeds?
Cc: kosaki.motohiro@jp.fujitsu.com, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
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Date: Tue,  5 Oct 2010 10:28:44 +0900 (JST)
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> 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?