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

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Message-Id: <20101005113840.28C9.A69D9226@jp.fujitsu.com>
Date:	Tue,  5 Oct 2010 11:37:24 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	kosaki.motohiro@...fujitsu.com, 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.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
 fs/binfmt_elf.c |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 535e763..ee235dd 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -74,8 +74,6 @@ static struct linux_binfmt elf_format = {
 		.hasvdso	= 1
 };
 
-#define BAD_ADDR(x) ((unsigned long)(x) >= TASK_SIZE)
-
 static int set_brk(unsigned long start, unsigned long end)
 {
 	start = ELF_PAGEALIGN(start);
@@ -85,7 +83,7 @@ static int set_brk(unsigned long start, unsigned long end)
 		down_write(&current->mm->mmap_sem);
 		addr = do_brk(start, end - start);
 		up_write(&current->mm->mmap_sem);
-		if (BAD_ADDR(addr))
+		if (IS_ERR_VALUE(addr))
 			return addr;
 	}
 	current->mm->start_brk = current->mm->brk = end;
@@ -345,7 +343,7 @@ static unsigned long elf_map(struct file *filep, unsigned long addr,
 	if (total_size) {
 		total_size = ELF_PAGEALIGN(total_size);
 		map_addr = do_mmap(filep, addr, total_size, prot, type, off);
-		if (!BAD_ADDR(map_addr))
+		if (!IS_ERR_VALUE(map_addr))
 			do_munmap(current->mm, map_addr+size, total_size-size);
 	} else
 		map_addr = do_mmap(filep, addr, size, prot, type, off);
-- 
1.6.5.2




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