Re: [PATCH v4 5.10/5.15] ata: libata-scsi: check cdb length for VARIABLE_LENGTH_CMD commands

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

On 6/27/24 06:13, Mikhail Ukhin wrote:
> 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.

This sentence is not needed in the commit message. That is a discussion to have
when applying (or not) the patch.

> 
> 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>

Please send patches for libata to the ata maintainers (Niklas and myself).
Use scripts/get_maintainer.pl And you will get our addresses and see that there
is no need to spam Jens with libata patches.

> ---
>  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.
>  v4: Extra opcode check removed.
>  drivers/ata/libata-scsi.c | 3 +++
>  1 file changed, 3 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]);
> 
> +	if (scmd->cmd_len < 32)

Given that the only service action supported is ATA_32, this check should be

	if (scmd->cmd_len != 32

> +		return 1;
> +
>  	/*
>  	 * if service action represents a ata pass-thru(32) command,
>  	 * then pass it to ata_scsi_pass_thru handler.
> --
> 2.25.1
> 

-- 
Damien Le Moal
Western Digital Research