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) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
