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

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Message-ID: <20201015063137.GA3668@jagdpanzerIV.localdomain>
Date:   Thu, 15 Oct 2020 15:31:37 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <mladek.petr@...il.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        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 (20/10/14 19:50), Petr Mladek 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.

Acked-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

	-ss