netdev - Re: [BUG] net: rds: rds_send

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Date:   Sun, 14 Mar 2021 16:05:21 +0300
From:   Fatih Yildirim <yildirim.fatih@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     santosh.shilimkar@...cle.com, davem@...emloft.net, kuba@...nel.org,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        rds-devel@....oracle.com, linux-kernel@...r.kernel.org
Subject: Re: [BUG] net: rds: rds_send_probe memory leak

On Sun, 2021-03-14 at 13:44 +0100, Greg KH wrote:
> On Sun, Mar 14, 2021 at 03:19:05PM +0300, Fatih Yildirim wrote:
> > On Sun, 2021-03-14 at 09:36 +0100, Greg KH wrote:
> > > On Sun, Mar 14, 2021 at 11:23:10AM +0300, Fatih Yildirim wrote:
> > > > Hi Santosh,
> > > > 
> > > > I've been working on a memory leak bug reported by syzbot.
> > > > https://syzkaller.appspot.com/bug?id=39b72114839a6dbd66c1d2104522698a813f9ae2
> > > > 
> > > > It seems that memory allocated in rds_send_probe function is
> > > > not
> > > > freed.
> > > > 
> > > > Let me share my observations.
> > > > rds_message is allocated at the beginning of rds_send_probe
> > > > function.
> > > > Then it is added to cp_send_queue list of rds_conn_path and
> > > > refcount
> > > > is increased by one.
> > > > Next, in rds_send_xmit function it is moved from cp_send_queue
> > > > list
> > > > to
> > > > cp_retrans list, and again refcount is increased by one.
> > > > Finally in rds_loop_xmit function refcount is increased by one.
> > > > So, total refcount is 4.
> > > > However, rds_message_put is called three times, in
> > > > rds_send_probe,
> > > > rds_send_remove_from_sock and rds_send_xmit functions. It seems
> > > > that
> > > > one more rds_message_put is needed.
> > > > Would you please check and share your comments on this issue?
> > > 
> > > Do you have a proposed patch that syzbot can test to verify if
> > > this
> > > is
> > > correct or not?
> > > 
> > > thanks,
> > > 
> > > gre gk-h
> > 
> > Hi Greg,
> > 
> > Actually, using the .config and the C reproducer, syzbot reports
> > the
> > memory leak in rds_send_probe function. Also by enabling
> > CONFIG_RDS_DEBUG=y, the debug messages indicates the similar as I
> > mentioned above. To give an example, below is the RDS_DEBUG
> > messages.
> > Allocated address 000000008a7476e5 has initial ref_count 1. Then
> > there
> > are three rds_message_addref calls for the same address making the
> > refcount 4, but only three rds_message_put calls which leave the
> > address still allocated.
> > 
> > [   60.570681] rds_message_addref(): addref rm 000000008a7476e5 ref
> > 1
> > [   60.570707] rds_message_put(): put rm 000000008a7476e5 ref 2
> > [   60.570845] rds_message_addref(): addref rm 000000008a7476e5 ref
> > 1
> > [   60.570870] rds_message_addref(): addref rm 000000008a7476e5 ref
> > 2
> > [   60.570960] rds_message_put(): put rm 000000008a7476e5 ref 3
> > [   60.570995] rds_message_put(): put rm 000000008a7476e5 ref 2
> > 
> 
> Ok, so the next step is to try your proposed change to see if it
> works
> or not.  What prevents you from doign that?
> 
> No need to ask people if your analysis of an issue is true or not, no
> maintainer or developer usually has the time to deal with that.  We
> much
> rather would like to see patches of things you have tested to resolve
> issues.
> 
> thanks,
> 
> greg k-h

Hi Greg,

I also would like to come with a patch to resolve the issue as well.
But couldn't figure out so far. I just would like to have a review or a
suggestion from an expert in order to move forward.
Anyway, I'm still working on it and hope to find a solution.
Will appreciate any comment, suggestion on the issue.

Thanks,
Fatih