netdev - Re: KASAN: use-after-free Read in __rhashtable

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Date:   Fri, 24 Aug 2018 19:37:00 -0400
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+8967084bcac563795dc6@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>, linux-rdma@...r.kernel.org,
        netdev <netdev@...r.kernel.org>, rds-devel@....oracle.com,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: use-after-free Read in __rhashtable_lookup (2)

On (08/24/18 16:10), Dmitry Vyukov wrote:
> You need a colon after dup.

I see.

> But this can't possibly be a dup of that bug. That bug was fixed in February:

Apologies, I unknowingly made a mistake in my 
syzbot-tiquette in that case,

I did not intend to *close* the bug as a dup, I was
merely trying to indicate that this is yet another 
manifestation of the original report with subject
"KASAN: use-after-free Read in rds_find_bound"

All of these problems are happening because we are missing
a synchronize_net() in rds_release.

A full description of the race conditon can be found in
https://www.spinics.net/lists/netdev/msg475074.html

If rds_release is going to nuke the rds_socket
it needs to sychronize_net() with other threads that may be
looking up the bind_hash_table. If we dont do that,
all of these "use-after-free" races can happen.
As long as we dont have the synchronize_net() we are
missing a big (and standard) bit of RCU synchronization.

--Sowmini