netdev - Re: [PATCH net-next] rxrpc: uninitialized variable in rxrpc_send_ack

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Message-ID: <Y3YOUQM/ldDe/sgC@kadam>
Date:   Thu, 17 Nov 2022 13:34:57 +0300
From:   Dan Carpenter <error27@...il.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Marc Dionne <marc.dionne@...istor.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-afs@...ts.infradead.org,
        netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net-next] rxrpc: uninitialized variable in
 rxrpc_send_ack_packet()

On Thu, Nov 17, 2022 at 09:44:24AM +0000, David Howells wrote:
> Dan Carpenter <error27@...il.com> wrote:
> 
> > The "pkt" was supposed to have been deleted in a previous patch.  It
> > leads to an uninitialized variable bug.
> 
> Weird.  I don't get a compiler warning and the kernel doesn't crash, despite
> transmitting millions of acks.
> 
> If I disassemble the built code, I see:
> 
>    0xffffffff81b09e89 <+723>:   xor    %edi,%edi
>    0xffffffff81b09e8b <+725>:   call   0xffffffff811c0bc1 <kfree>
> 
> I'm not sure why it's sticking 0 in EDI, though.

We disabled GCC's check for uninitialized variables.  It could be that
you have the .config to automatically zero out stack variables.

CONFIG_CC_HAS_AUTO_VAR_INIT_PATTERN=y
CONFIG_CC_HAS_AUTO_VAR_INIT_ZERO_BARE=y
CONFIG_CC_HAS_AUTO_VAR_INIT_ZERO=y

regards,
dan carpenter