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uretprobes: Limit the depth of return probe nestedness

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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>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
This commit is contained in:
Anton Arapov 2013-04-03 18:00:37 +02:00 committed by Oleg Nesterov
parent fec8898d86
commit ded49c5530
2 changed files with 14 additions and 0 deletions
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3
include/linux/uprobes.h
View File

@ -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;

11
kernel/events/uprobes.c
View File

@ -1404,6 +1404,13 @@ 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;
@ -1439,6 +1446,8 @@ 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;
@ -1681,6 +1690,8 @@ static bool handle_trampoline(struct pt_regs *regs)
if (!chained)
break;
utask->depth--;
BUG_ON(!ri);
}