linux-kernel - Re: [PATCH] printk: ringbuffer: Wrong data pointer when appending small string

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Message-ID: <20201015122246.GD8871@alley>
Date:   Thu, 15 Oct 2020 14:22:46 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Linux-Next Mailing List <linux-next@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        open list <linux-kernel@...r.kernel.org>,
        lkft-triage@...ts.linaro.org, LTP List <ltp@...ts.linux.it>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Naresh Kamboju <naresh.kamboju@...aro.org>
Subject: Re: [PATCH] printk: ringbuffer: Wrong data pointer when appending
 small string

On Wed 2020-10-14 19:50:54, Petr Mladek wrote:
> data_realloc() returns wrong data pointer when the block is wrapped and
> the size is not increased. It might happen when pr_cont() wants to
> add only few characters and there is already a space for them because
> of alignment.
> 
> It might cause writing outsite the buffer. It has been detected by LTP
> tests with KASAN enabled:
> 
> Link: https://lore.kernel.org/r/CA+G9fYt46oC7-BKryNDaaXPJ9GztvS2cs_7GjYRjanRi4+ryCQ@mail.gmail.com
> Fixes: 4cfc7258f876a7feba673ac ("printk: ringbuffer: add finalization/extension support")
> Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org>
> Signed-off-by: Petr Mladek <pmladek@...e.com>

The patch is committed into printk/linux.git, branch for-5.10-fixup.

I am going to send a pull request with it tomorrow unless something
happens in the meantime.

Best Regards,
Petr