linux-kernel - Re: BUG: KASAN: use-after-scope in ep

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Date:   Thu, 30 Nov 2017 13:57:16 -0500
From:   Jason Baron <jbaron@...mai.com>
To:     Fengguang Wu <fengguang.wu@...el.com>
Cc:     Shakeel Butt <shakeelb@...gle.com>, Lee Duncan <lduncan@...e.com>,
        Chris Leech <cleech@...hat.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        open-iscsi@...glegroups.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, lkp@...org
Subject: Re: BUG: KASAN: use-after-scope in ep_poll+0x5cd/0xc90

Hi,

On 11/29/2017 10:41 PM, Fengguang Wu wrote:
> Hello,
> 
> FYI this happens in mainline kernel 4.15.0-rc1.
> It looks a new regression and bisect is on the way.
> 
> It occurs in 3 out of 3 boots.
> 
> [   35.704690] init: Failed to create pty - disabling logging for job
> [   35.706676] init: Temporary process spawn error: No such file or directory
> [   35.731988] init: Failed to create pty - disabling logging for job
> [   35.734084] init: Temporary process spawn error: No such file or directory
> [   35.737946] ==================================================================
> [   35.739635] BUG: KASAN: use-after-scope in ep_poll+0x5cd/0xc90:
> 						ep_send_events at fs/eventpoll.c:1700
> 						 (inlined by) ep_poll at fs/eventpoll.c:1829

This seems to be pointing out that 'struct ep_send_events_data esed' on
line 1700 (below) is being used out of scope?

1697 static int ep_send_events(struct eventpoll *ep,

1698                           struct epoll_event __user *events, int
maxevents)
1699 {

1700         struct ep_send_events_data esed;

1701

1702         esed.maxevents = maxevents;

1703         esed.events = events;

1704

1705         return ep_scan_ready_list(ep, ep_send_events_proc, &esed,
0, false);

There have been some epoll changes new to 4.15 that would be tempting to
blame, but I don't see anything obvious wrong and the usage of 'esed'
hasn't really changed.

So I'm curious to see where your bisect leads. There also seems to be a
number of reports of false positives with KASAN out of scope reported
recently, so I'm not sure if this could be a false positive?

Thanks,

-Jason