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

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Date:   Wed, 28 Sep 2022 13:49:19 +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 07:43:38PM +0900, asmadeus@...ewreck.org wrote:
> Leon Romanovsky wrote on Wed, Sep 28, 2022 at 01:07:23PM +0300:
> > The bug is in commit 3ff51294a055 ("9p: p9_client_create: use p9_client_destroy on failure").
> 
> Thanks for looking
> 
> > It is wrong to call to p9_client_destroy() if clnt->trans_mod->create fails.
> 
> hmm that's a bit broad :)
> 
> 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.

> 
> I'll send a patch and credit you in Reported-by unless you don't want
> to.
> 
> -- 
> Dominique