netdev - Re: [syzbot] KASAN: use-after-free Read in rdma

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Date:   Wed, 28 Sep 2022 14:54:03 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     asmadeus@...ewreck.org
Cc:     syzbot <syzbot+67d13108d855f451cafc@...kaller.appspotmail.com>,
        davem@...emloft.net, edumazet@...gle.com, ericvh@...il.com,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        linux_oss@...debyte.com, lucho@...kov.net, netdev@...r.kernel.org,
        pabeni@...hat.com, syzkaller-bugs@...glegroups.com,
        v9fs-developer@...ts.sourceforge.net
Subject: Re: [syzbot] KASAN: use-after-free Read in rdma_close

On Wed, Sep 28, 2022 at 08:23:14PM +0900, asmadeus@...ewreck.org wrote:
> Leon Romanovsky wrote on Wed, Sep 28, 2022 at 01:49:19PM +0300:
> > > But I agree I did get that wrong: trans_mod->close() wasn't called if
> > > create failed.
> > > We do want the idr_for_each_entry() that is in p9_client_destroy so
> > > rather than revert the commit (fix a bug, create a new one..) I'd rather
> > > split it out in an internal function that takes a 'bool close' or
> > > something to not duplicate the rest.
> > > (Bit of a nitpick, sure)
> > 
> > Please do proper unwind without extra variable.
> > 
> > Proper unwind means that you will call to symmetrical functions in
> > destroy as you used in create:
> > alloc -> free
> > create -> close
> > e.t.c
> > 
> > When you use some global function like you did, there is huge chance
> > to see unwind bugs.
> 
> No.

Let's agree to disagree.

> 
> Duplicating complicated cleanup code leads to leaks like we used to
> have; that destroy function already frees up things in the right order.

It is pretty straightforward code, nothing complex there.

Just pause for a minute, and ask yourself how totally random guy who
looked on this syzbot bug just because RDMA name in it, found the issue
so quickly.

I will give a hint, I saw not symmetrical error unwind in call trace.

Thanks