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

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Date:	Mon, 4 Oct 2010 22:31:46 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	kosaki.motohiro@...fujitsu.com
Cc:	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.
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