In message <20100209154141.03F0.A69D9226@xxxxxxxxxxxxxx> you wrote:
> > When reserving stack space for a new process, make sure we're not
> > attempting to expand the stack by more than rlimit allows.
> >
> > This fixes a bug caused by b6a2fea39318e43fee84fa7b0b90d68bed92d2ba "mm:
> > variable length argument support" and unmasked by
> > fc63cf237078c86214abcb2ee9926d8ad289da9b "exec: setup_arg_pages() fails
> > to return errors". This bug means when limiting the stack to less the
> > 20*PAGE_SIZE (eg. 80K on 4K pages or 'ulimit -s 79') all processes will
> > be killed before they start. This is particularly bad with 64K pages,
> > where a ulimit below 1280K will kill every process.
> >
> > Signed-off-by: Michael Neuling <mikey@xxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxx
> > ---
> > Attempts to answer comments from Kosaki Motohiro.
> >
> > Tested on PPC only, hence !CONFIG_STACK_GROWSUP. Someone should
> > probably ACK for an arch with CONFIG_STACK_GROWSUP.
> >
> > As noted, stable needs the same patch, but 2.6.32 doesn't have the
> > rlimit() helper.
> >
> > fs/exec.c | 21 ++++++++++++++++++---
> > 1 file changed, 18 insertions(+), 3 deletions(-)
> >
> > Index: linux-2.6-ozlabs/fs/exec.c
> > ===================================================================
> > --- linux-2.6-ozlabs.orig/fs/exec.c
> > +++ linux-2.6-ozlabs/fs/exec.c
> > @@ -555,6 +555,7 @@ static int shift_arg_pages(struct vm_are
> > }
> >
> > #define EXTRA_STACK_VM_PAGES 20 /* random */
> > +#define ALIGN_DOWN(addr,size) ((addr)&(~((size)-1)))
> >
> > /*
> > * Finalizes the stack vm_area_struct. The flags and permissions are updat
ed,
> > @@ -570,7 +571,7 @@ int setup_arg_pages(struct linux_binprm
> > struct vm_area_struct *vma = bprm->vma;
> > struct vm_area_struct *prev = NULL;
> > unsigned long vm_flags;
> > - unsigned long stack_base;
> > + unsigned long stack_base, stack_expand, stack_expand_lim, stack_size;
> >
> > #ifdef CONFIG_STACK_GROWSUP
> > /* Limit stack size to 1GB */
> > @@ -627,10 +628,24 @@ int setup_arg_pages(struct linux_binprm
> > goto out_unlock;
> > }
> >
> > + stack_expand = EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> > + stack_size = vma->vm_end - vma->vm_start;
> > + if (rlimit(RLIMIT_STACK) < stack_size)
> > + stack_expand_lim = 0; /* don't shrick the stack */
> > + else
> > + /*
> > + * Align this down to a page boundary as expand_stack
> > + * will align it up.
> > + */
> > + stack_expand_lim = ALIGN_DOWN(rlimit(RLIMIT_STACK) - stack_size
,
> > + PAGE_SIZE);
> > + /* Initial stack must not cause stack overflow. */
> > + if (stack_expand > stack_expand_lim)
> > + stack_expand = stack_expand_lim;
> > #ifdef CONFIG_STACK_GROWSUP
> > - stack_base = vma->vm_end + EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> > + stack_base = vma->vm_end + stack_expand;
> > #else
> > - stack_base = vma->vm_start - EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> > + stack_base = vma->vm_start - stack_expand;
> > #endif
> > ret = expand_stack(vma, stack_base);
> > if (ret)
>
> Umm.. It looks correct. but the nested complex if statement seems a bit ugly.
> Instead, How about following?
I don't like the duplicated code in the #ifdef/else but I can live with it.
> note: it's untested.
Works for me on ppc64 with 4k and 64k pages. Thanks!
I'd still like someone with a CONFIG_STACK_GROWSUP arch to test/ACK it
as well.
Mikey
>
>
>
> ===============
> From: Michael Neuling <mikey@xxxxxxxxxxx>
> Subject: Restrict initial stack space expansion to rlimit
>
> When reserving stack space for a new process, make sure we're not
> attempting to expand the stack by more than rlimit allows.
>
> This fixes a bug caused by b6a2fea39318e43fee84fa7b0b90d68bed92d2ba "mm:
> variable length argument support" and unmasked by
> fc63cf237078c86214abcb2ee9926d8ad289da9b "exec: setup_arg_pages() fails
> to return errors". This bug means when limiting the stack to less the
> 20*PAGE_SIZE (eg. 80K on 4K pages or 'ulimit -s 79') all processes will
> be killed before they start. This is particularly bad with 64K pages,
> where a ulimit below 1280K will kill every process.
>
> [kosaki.motohiro@xxxxxxxxxxxxxx: cleanups]
> Signed-off-by: Michael Neuling <mikey@xxxxxxxxxxx>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxx
> ---
> Attempts to answer comments from Kosaki Motohiro.
>
> Tested on PPC only, hence !CONFIG_STACK_GROWSUP. Someone should
> probably ACK for an arch with CONFIG_STACK_GROWSUP.
>
> As noted, stable needs the same patch, but 2.6.32 doesn't have the
> rlimit() helper.
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 6f7fb0c..325bad4 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -573,6 +573,9 @@ int setup_arg_pages(struct linux_binprm *bprm,
> struct vm_area_struct *prev = NULL;
> unsigned long vm_flags;
> unsigned long stack_base;
> + unsigned long stack_size;
> + unsigned long stack_expand;
> + unsigned long rlim_stack;
>
> #ifdef CONFIG_STACK_GROWSUP
> /* Limit stack size to 1GB */
> @@ -629,10 +632,27 @@ int setup_arg_pages(struct linux_binprm *bprm,
> goto out_unlock;
> }
>
> + stack_expand = EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> + stack_size = vma->vm_end - vma->vm_start;
> + /*
> + * Align this down to a page boundary as expand_stack
> + * will align it up.
> + */
> + rlim_stack = rlimit(RLIMIT_STACK) & PAGE_MASK;
> + if (rlim_stack < stack_size)
> + rlim_stack = stack_size;
> #ifdef CONFIG_STACK_GROWSUP
> - stack_base = vma->vm_end + EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> + if (stack_size + stack_expand > rlim_stack) {
> + stack_base = vma->vm_start + rlim_stack;
> + } else {
> + stack_base = vma->vm_end + stack_expand;
> + }
> #else
> - stack_base = vma->vm_start - EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> + if (stack_size + stack_expand > rlim_stack) {
> + stack_base = vma->vm_end - rlim_stack;
> + } else {
> + stack_base = vma->vm_start - stack_expand;
> + }
> #endif
> ret = expand_stack(vma, stack_base);
> if (ret)
>
>
>
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