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

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Message-ID: <875z7bhks1.fsf@jogness.linutronix.de>
Date:   Thu, 15 Oct 2020 12:05:42 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <mladek.petr@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        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 2020-10-15, Sergey Senozhatsky <sergey.senozhatsky@...il.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@...utronix.de>