linux-kernel - Re: [PATCH 0/2] introduce DUMP_PREFIX

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Date:   Tue, 19 Jan 2021 12:18:17 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Timur Tabi <timur@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        Petr Mladek <pmladek@...e.com>, roman.fietze@...na.com,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>, linux-mm@...ck.org,
        Akinobu Mita <akinobu.mita@...il.com>
Subject: Re: [PATCH 0/2] introduce DUMP_PREFIX_UNHASHED for hex dumps

On 1/19/21 11:45 AM, Kees Cook wrote:
> 
> How about this so the base address is hashed once, with the offset added
> to it for each line instead of each line having a "new" hash that makes
> no sense:

Yes, good patch. Should have been like this to begin with IMO.

> diff --git a/lib/hexdump.c b/lib/hexdump.c
> index 9301578f98e8..20264828752d 100644
> --- a/lib/hexdump.c
> +++ b/lib/hexdump.c
> @@ -242,12 +242,17 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
>  		    const void *buf, size_t len, bool ascii)
>  {
>  	const u8 *ptr = buf;
> +	const u8 *addr;
>  	int i, linelen, remaining = len;
>  	unsigned char linebuf[32 * 3 + 2 + 32 + 1];
>  
>  	if (rowsize != 16 && rowsize != 32)
>  		rowsize = 16;
>  
> +	if (prefix_type == DUMP_PREFIX_ADDRESS &&
> +	    ptr_to_hashval(ptr, &addr))
> +		addr = 0;
> +
>  	for (i = 0; i < len; i += rowsize) {
>  		linelen = min(remaining, rowsize);
>  		remaining -= rowsize;
> @@ -258,7 +263,7 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
>  		switch (prefix_type) {
>  		case DUMP_PREFIX_ADDRESS:
>  			printk("%s%s%p: %s\n",
> -			       level, prefix_str, ptr + i, linebuf);
> +			       level, prefix_str, addr + i, linebuf);

Is 'addr' always set here?
It is only conditionally set above.

>  			break;
>  		case DUMP_PREFIX_OFFSET:
>  			printk("%s%s%.8x: %s\n", level, prefix_str, i, linebuf);
> 
> -Kees
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#p-format-specifier
> 


-- 
~Randy
"He closes his eyes and drops the goggles.  You can't get hurt
by looking at a bitmap.  Or can you?"
(Neal Stephenson: Snow Crash)