> 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 updated,
> @@ -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?
note: it's untested.
===============
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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