Restrict stack space reservation to rlimit

apkm, linus: this or something like it needs to go into 2.6.33 (& 32) to
fix 'ulimit -s'.  

Mikey

[PATCH] Restrict stack space reservation to rlimit

When reserving stack space for a new process, make sure we're not
attempting to allocate more than rlimit allows.

Also, reserve the same stack size independent of page size.

This fixes a bug unmasked by fc63cf237078c86214abcb2ee9926d8ad289da9b

Signed-off-by: Michael Neuling <mikey@neuling.org>
Cc: Anton Blanchard <anton@samba.org>
Cc: stable@kernel.org
---
 fs/exec.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Hi

> apkm, linus: this or something like it needs to go into 2.6.33 (& 32) to
> fix 'ulimit -s'.  

"fix ulimit -s" is too cool explanation ;-)
we are not ESPer. please consider to provide what bug is exist.


> Mikey
> 
> [PATCH] Restrict stack space reservation to rlimit
> 
> When reserving stack space for a new process, make sure we're not
> attempting to allocate more than rlimit allows.
> 
> Also, reserve the same stack size independent of page size.

Why do we need page size independent stack size? It seems to have
compatibility breaking risk.


> 
> This fixes a bug unmasked by fc63cf237078c86214abcb2ee9926d8ad289da9b
> 
> Signed-off-by: Michael Neuling <mikey@neuling.org>
> Cc: Anton Blanchard <anton@samba.org>
> Cc: stable@kernel.org
> ---
>  fs/exec.c |    9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> Index: clone1/fs/exec.c
> ===================================================================
> --- clone1.orig/fs/exec.c
> +++ clone1/fs/exec.c
> @@ -554,7 +554,7 @@ static int shift_arg_pages(struct vm_are
>  	return 0;
>  }
>  
> -#define EXTRA_STACK_VM_PAGES	20	/* random */
> +#define EXTRA_STACK_VM_SIZE	81920UL	/* randomly 20 4K pages */
>  
>  /*
>   * Finalizes the stack vm_area_struct. The flags and permissions are updated,
> @@ -627,10 +627,13 @@ int setup_arg_pages(struct linux_binprm 
>  			goto out_unlock;
>  	}
>  
> +	stack_base = min(EXTRA_STACK_VM_SIZE,
> +			 current->signal->rlim[RLIMIT_STACK].rlim_cur) -
> +		PAGE_SIZE;
>  #ifdef CONFIG_STACK_GROWSUP
> -	stack_base = vma->vm_end + EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> +	stack_base = vma->vm_end + stack_base;
>  #else
> -	stack_base = vma->vm_start - EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> +	stack_base = vma->vm_start - stack_base;
>  #endif
>  	ret = expand_stack(vma, stack_base);
>  	if (ret)
> --
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Hi,

> Why do we need page size independent stack size? It seems to have
> compatibility breaking risk.

I don't think so. The current behaviour is clearly wrong, we dont need a
16x larger stack just because you went from a 4kB to a 64kB base page
size. The user application stack usage is the same in both cases.

Anton

>  
> Hi,
> 
> > Why do we need page size independent stack size? It seems to have
> > compatibility breaking risk.
> 
> I don't think so. The current behaviour is clearly wrong, we dont need a
> 16x larger stack just because you went from a 4kB to a 64kB base page
> size. The user application stack usage is the same in both cases.

I didn't discuss which behavior is better. Michael said he want to apply
his patch to 2.6.32 & 2.6.33. stable tree never accept the breaking
compatibility patch.

Your answer doesn't explain why can't we wait it until next merge window.


btw, personally, I like page size indepent stack size. but I'm not sure
why making stack size independency is related to bug fix.

Hi,

> I didn't discuss which behavior is better. Michael said he want to apply
> his patch to 2.6.32 & 2.6.33. stable tree never accept the breaking
> compatibility patch.
> 
> Your answer doesn't explain why can't we wait it until next merge window.
> 
> 
> btw, personally, I like page size indepent stack size. but I'm not sure
> why making stack size independency is related to bug fix.

OK sorry, I misunderstood your initial mail. I agree fixing the bit that
regressed in 2.6.32 is the most important thing. The difference in page size is
clearly wrong but since it isn't a regression we could probably live with it
until 2.6.34

Anton

> 
> Hi,
> 
> > I didn't discuss which behavior is better. Michael said he want to apply
> > his patch to 2.6.32 & 2.6.33. stable tree never accept the breaking
> > compatibility patch.
> > 
> > Your answer doesn't explain why can't we wait it until next merge window.
> > 
> > 
> > btw, personally, I like page size indepent stack size. but I'm not sure
> > why making stack size independency is related to bug fix.
> 
> OK sorry, I misunderstood your initial mail. I agree fixing the bit that
> regressed in 2.6.32 is the most important thing. The difference in page size is
> clearly wrong but since it isn't a regression we could probably live with it
> until 2.6.34

thanks!