Re: [PATCH] ata: libata-sff: Ensure that we cannot write outside the allocated buffer

[Damien Le Moal <dlemoal@kernel.org>]

On 1/24/25 23:11, Niklas Cassel wrote:
> reveliofuzzing reported that a SCSI_IOCTL_SEND_COMMAND ioctl with out_len
> set to 0xd42, SCSI command set to ATA_16 PASS-THROUGH, ATA command set to
> ATA_NOP, and protocol set to ATA_PROT_PIO, can cause ata_pio_sector() to
> write outside the allocated buffer, overwriting random memory.
> 
> While a ATA device is supposed to abort a ATA_NOP command, there does seem
> to be a bug either in libata-sff or QEMU, where either this status is not
> set, or the status is cleared before read by ata_sff_hsm_move().
> Anyway, that is most likely a separate bug.
> 
> Looking at __atapi_pio_bytes(), it already has a safety check to ensure
> that __atapi_pio_bytes() cannot write outside the allocated buffer.
> 
> Add a similar check to ata_pio_sector(), such that also ata_pio_sector()
> cannot write outside the allocated buffer.
> 
> Reported-by: reveliofuzzing <reveliofuzzing@gmail.com>
> Closes: https://lore.kernel.org/linux-ide/CA+-ZZ_jTgxh3bS7m+KX07_EWckSnW3N2adX3KV63y4g7M4CZ2A@mail.gmail.com/
> Signed-off-by: Niklas Cassel <cassel@kernel.org>

Looks good to me. But doesn't this need Fixes + Cc-stable tags ?

> ---
>  drivers/ata/libata-sff.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
> index 67f277e1c3bf..5a46c066abc3 100644
> --- a/drivers/ata/libata-sff.c
> +++ b/drivers/ata/libata-sff.c
> @@ -601,7 +601,7 @@ static void ata_pio_sector(struct ata_queued_cmd *qc)
>  {
>  	struct ata_port *ap = qc->ap;
>  	struct page *page;
> -	unsigned int offset;
> +	unsigned int offset, count;
>  
>  	if (!qc->cursg) {
>  		qc->curbytes = qc->nbytes;
> @@ -617,25 +617,27 @@ static void ata_pio_sector(struct ata_queued_cmd *qc)
>  	page = nth_page(page, (offset >> PAGE_SHIFT));
>  	offset %= PAGE_SIZE;
>  
> -	trace_ata_sff_pio_transfer_data(qc, offset, qc->sect_size);
> +	/* don't overrun current sg */
> +	count = min(qc->cursg->length - qc->cursg_ofs, qc->sect_size);
> +
> +	trace_ata_sff_pio_transfer_data(qc, offset, count);
>  
>  	/*
>  	 * Split the transfer when it splits a page boundary.  Note that the
>  	 * split still has to be dword aligned like all ATA data transfers.
>  	 */
>  	WARN_ON_ONCE(offset % 4);
> -	if (offset + qc->sect_size > PAGE_SIZE) {
> +	if (offset + count > PAGE_SIZE) {
>  		unsigned int split_len = PAGE_SIZE - offset;
>  
>  		ata_pio_xfer(qc, page, offset, split_len);
> -		ata_pio_xfer(qc, nth_page(page, 1), 0,
> -			     qc->sect_size - split_len);
> +		ata_pio_xfer(qc, nth_page(page, 1), 0, count - split_len);
>  	} else {
> -		ata_pio_xfer(qc, page, offset, qc->sect_size);
> +		ata_pio_xfer(qc, page, offset, count);
>  	}
>  
> -	qc->curbytes += qc->sect_size;
> -	qc->cursg_ofs += qc->sect_size;
> +	qc->curbytes += count;
> +	qc->cursg_ofs += count;
>  
>  	if (qc->cursg_ofs == qc->cursg->length) {
>  		qc->cursg = sg_next(qc->cursg);


-- 
Damien Le Moal
Western Digital Research