Re: [PATCH v3 5.10/5.15] ata: libata-scsi: check cdb length for VARIABLE_LENGTH_CMD commands

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

On 6/6/24 6:34 AM, Mikhail Ukhin wrote:
> No upstream commit exists for this patch.
> 
> Fuzzing of 5.10 stable branch reports a slab-out-of-bounds error in
> ata_scsi_pass_thru.
> 
> The error is fixed in 5.18 by commit ce70fd9a551a ("scsi: core: Remove the
> cmd field from struct scsi_request") upstream.
> Backporting this commit would require significant changes to the code so
> it is bettter to use a simple fix for that particular error.
> 
> The problem is that the length of the received SCSI command is not
> validated if scsi_op == VARIABLE_LENGTH_CMD. It can lead to out-of-bounds
> reading if the user sends a request with SCSI command of length less than
> 32.
> 
> Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
> 
> Signed-off-by: Artem Sadovnikov <ancowi69@gmail.com>
> Signed-off-by: Mikhail Ivanov <iwanov-23@bk.ru>
> Signed-off-by: Mikhail Ukhin <mish.uxin2012@yandex.ru>
> ---
>  v2: The new addresses were added and the text was updated.
>  v3: Checking has been moved to the function ata_scsi_var_len_cdb_xlat at
>  the request of Damien Le Moal
>  drivers/ata/libata-scsi.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index dfa090ccd21c..38488bd813d1 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -3948,7 +3948,11 @@ static unsigned int ata_scsi_var_len_cdb_xlat(struct ata_queued_cmd *qc)
>  	struct scsi_cmnd *scmd = qc->scsicmd;
>  	const u8 *cdb = scmd->cmnd;
>  	const u16 sa = get_unaligned_be16(&cdb[8]);
> +	u8 scsi_op = scmd->cmnd[0];
>  
> +	if (scsi_op == VARIABLE_LENGTH_CMD && scmd->cmd_len < 32)

This functions is called only when the opcode is VARIABLE_LENGTH_CMD. So there
is no need to check that again.

> +        	return 1;
> +	
>  	/*
>  	 * if service action represents a ata pass-thru(32) command,
>  	 * then pass it to ata_scsi_pass_thru handler.

-- 
Damien Le Moal
Western Digital Research