linux-kernel - Re: [PATCH] uprobes: Fix limiting un-nested return probes

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Date:	Sun, 8 Sep 2013 18:32:32 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Hemant Kumar Shaw <hkshaw@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, Mikhail.Kulemin@...ibm.com,
	srikar@...ux.vnet.ibm.com, peterz@...radead.org, mingo@...hat.com,
	anton@...hat.com, systemtap@...rceware.org,
	masami.hiramatsu.pt@...achi.com
Subject: Re: [PATCH] uprobes: Fix limiting un-nested return probes

Sorry for delay, vacation.

On 09/03, Hemant Kumar Shaw wrote:
>
> There exists a limit to the number of nested return probes. The current limit is 64.
> However this limit is getting enforced on even non nested return probes.
> Hence, registering 64 independent non nested return probes results in failure of
> return probes on the same task. The problem is utask->depth is getting incremented
> unconditionally but decremented only if chained.

Hmm. I'll try to recheck later, but at first glance this logic is indeed
wrong, thanks.

> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1442,7 +1442,8 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
>  	ri->orig_ret_vaddr = orig_ret_vaddr;
>  	ri->chained = chained;
>  
> -	utask->depth++;
> +	if (chained)
> +		utask->depth++;

Not sure, but I can be easily wrong... afaics we need something like below, no?

Anton?

Oleg.

--- x/kernel/events/uprobes.c
+++ x/kernel/events/uprobes.c
@@ -1682,12 +1682,10 @@ static bool handle_trampoline(struct pt_
 		tmp = ri;
 		ri = ri->next;
 		kfree(tmp);
+		utask->depth--;
 
 		if (!chained)
 			break;
-
-		utask->depth--;
-
 		BUG_ON(!ri);
 	}
 

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