linux-kernel - Re: [tip: efi/core] efi: cper: fix scnprintf() use in cper_mem_err

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Message-ID: <d18d2c6fd87f552def3210930da34fd276b4fd6d.camel@perches.com>
Date:   Sat, 28 Aug 2021 04:22:24 -0700
From:   Joe Perches <joe@...ches.com>
To:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Ard Biesheuvel <ardb@...nel.org>, x86@...nel.org
Subject: Re: [tip: efi/core] efi: cper: fix scnprintf() use in
 cper_mem_err_location()

On Sat, 2021-08-28 at 10:37 +0000, tip-bot2 for Rasmus Villemoes wrote:
> The following commit has been merged into the efi/core branch of tip:
[]
> efi: cper: fix scnprintf() use in cper_mem_err_location()
> 
> The last two if-clauses fail to update n, so whatever they might have
> written at &msg[n] would be cut off by the final nul-termination.
> 
> That nul-termination is redundant; scnprintf(), just like snprintf(),
> guarantees a nul-terminated output buffer, provided the buffer size is
> positive.
> 
> And there's no need to discount one byte from the initial buffer;
> vsnprintf() expects to be given the full buffer size - it's not going
> to write the nul-terminator one beyond the given (buffer, size) pair.
[]
> diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
[]
> @@ -221,7 +221,7 @@ static int cper_mem_err_location(struct cper_mem_err_compact *mem, char *msg)
>  		return 0;
>  
> 
>  	n = 0;
> -	len = CPER_REC_LEN - 1;
> +	len = CPER_REC_LEN;
>  	if (mem->validation_bits & CPER_MEM_VALID_NODE)
>  		n += scnprintf(msg + n, len - n, "node: %d ", mem->node);
>  	if (mem->validation_bits & CPER_MEM_VALID_CARD)

[etc...]

Is this always single threaded?

It doesn't seem this is safe for reentry as the output buffer
being written into is a single static

static char rcd_decode_str[CPER_REC_LEN];