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SubjectRe: [PATCH v1 7/9] uretprobes: Limit the depth of return probe nestedness
* Anton Arapov <anton@redhat.com> [2013-04-03 18:00:37]:

> Unlike the kretprobes we can't trust userspace, thus must have
> protection from user space attacks. User-space have "unlimited"
> stack, and this patch limits the return probes nestedness as a
> simple remedy for it.
>
> Note that this implementation leaks return_instance on siglongjmp
> until exit()/exec().
>
> The intention is to have KISS and bare minimum solution for the
> initial implementation in order to not complicate the uretprobes
> code.
>
> In the future we may come up with more sophisticated solution that
> remove this depth limitation. It is not easy task and lays beyond
> this patchset.
>
> Signed-off-by: Anton Arapov <anton@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
> include/linux/uprobes.h | 3 +++
> kernel/events/uprobes.c | 11 +++++++++++
> 2 files changed, 14 insertions(+)
>
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 5f8960e..d7bcf10 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -38,6 +38,8 @@ struct inode;
> #define UPROBE_HANDLER_REMOVE 1
> #define UPROBE_HANDLER_MASK 1
>
> +#define MAX_URETPROBE_DEPTH 64
> +
> enum uprobe_filter_ctx {
> UPROBE_FILTER_REGISTER,
> UPROBE_FILTER_UNREGISTER,
> @@ -72,6 +74,7 @@ struct uprobe_task {
> struct arch_uprobe_task autask;
>
> struct return_instance *return_instances;
> + unsigned int depth;
> struct uprobe *active_uprobe;
>
> unsigned long xol_vaddr;
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index d129c1d..489f5e3 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1381,6 +1381,13 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
> if (!utask)
> return;
>
> + if (utask->depth >= MAX_URETPROBE_DEPTH) {
> + printk_ratelimited(KERN_INFO "uprobe: omit uretprobe due to"
> + " nestedness limit pid/tgid=%d/%d\n",
> + current->pid, current->tgid);
> + return;
> + }
> +
> ri = kzalloc(sizeof(struct return_instance), GFP_KERNEL);
> if (!ri)
> goto fail;
> @@ -1416,6 +1423,8 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
> ri->orig_ret_vaddr = orig_ret_vaddr;
> ri->chained = chained;
>
> + utask->depth++;
> +
> /* add instance to the stack */
> ri->next = utask->return_instances;
> utask->return_instances = ri;
> @@ -1652,6 +1661,8 @@ static bool handler_uretprobe(struct pt_regs *regs)
> if (!chained)
> break;
>
> + utask->depth--;
> +
> BUG_ON(!ri);
> }
>
> --
> 1.8.1.4
>

--
Thanks and Regards
Srikar Dronamraju



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