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From:   John Ogness <john.ogness@linutronix.de>
To:     Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Petr Mladek <mladek.petr@gmail.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linux-Next Mailing List <linux-next@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        open list <linux-kernel@vger.kernel.org>,
        lkft-triage@lists.linaro.org, LTP List <ltp@lists.linux.it>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Naresh Kamboju <naresh.kamboju@linaro.org>
Subject: Re: [PATCH] printk: ringbuffer: Wrong data pointer when appending small string
In-Reply-To: <20201015063137.GA3668@jagdpanzerIV.localdomain>
References: <CA+G9fYt46oC7-BKryNDaaXPJ9GztvS2cs_7GjYRjanRi4+ryCQ@mail.gmail.com> <20201014140514.GB17231@alley> <20201014151311.GB13775@alley> <20201014175051.GC13775@alley> <20201015063137.GA3668@jagdpanzerIV.localdomain>
Date:   Thu, 15 Oct 2020 12:05:42 +0206
Message-ID: <875z7bhks1.fsf@jogness.linutronix.de>
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On 2020-10-15, Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote:
>> diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
>> index 2493348a1631..24a960a89aa8 100644
>> --- a/kernel/printk/printk_ringbuffer.c
>> +++ b/kernel/printk/printk_ringbuffer.c
>> @@ -1125,7 +1125,10 @@ static char *data_realloc(struct printk_ringbuffer *rb,
>>  
>>  	/* If the data block does not increase, there is nothing to do. */
>>  	if (head_lpos - next_lpos < DATA_SIZE(data_ring)) {
>> -		blk = to_block(data_ring, blk_lpos->begin);
>> +		if (wrapped)
>> +			blk = to_block(data_ring, 0);
>> +		else
>> +			blk = to_block(data_ring, blk_lpos->begin);
>>  		return &blk->data[0];
>>  	}
>
> Great catch.

Indeed. I don't know how we missed that one. :-/

Reviewed-by: John Ogness <john.ogness@linutronix.de>