On Mon, 2017-05-08 at 18:07 +0000, Bart Van Assche wrote:
> On Sun, 2017-05-07 at 15:49 -0700, Nicholas A. Bellinger wrote:
> > On Thu, 2017-05-04 at 15:50 -0700, Bart Van Assche wrote:
> > > For VERIFY and WRITE AND VERIFY commands the size of the SCSI
> > > Data-Out buffer can differ from the size of the data area on
> > > the storage medium that is affected by the command. Make sure
> > > that the Data-Out buffer size is computed correctly. Apparently
> > > this part got dropped from my previous VERIFY / WRITE AND VERIFY
> > > patch before I posted it due to rebasing.
> > >
> > > Fixes: commit 0e2eb7d12eaa ("target: Fix VERIFY and WRITE VERIFY command parsing")
> > > Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
> > > Cc: Hannes Reinecke <hare@xxxxxxxx>
> > > Cc: Christoph Hellwig <hch@xxxxxx>
> > > Cc: Andy Grover <agrover@xxxxxxxxxx>
> > > Cc: David Disseldorp <ddiss@xxxxxxx>
> > > Cc: <stable@xxxxxxxxxxxxxxx>
> > > ---
> > > drivers/target/target_core_sbc.c | 5 +++--
> > > 1 file changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
> > > index a0ad618f1b1a..51489d96cb31 100644
> > > --- a/drivers/target/target_core_sbc.c
> > > +++ b/drivers/target/target_core_sbc.c
> > > @@ -888,9 +888,10 @@ static sense_reason_t sbc_parse_verify(struct se_cmd *cmd, int *sectors,
> > > sense_reason_t
> > > sbc_parse_cdb(struct se_cmd *cmd, struct sbc_ops *ops)
> > > {
> > > + enum { INVALID_SIZE = 1 };
> > > struct se_device *dev = cmd->se_dev;
> > > unsigned char *cdb = cmd->t_task_cdb;
> > > - unsigned int size;
> > > + unsigned int size = INVALID_SIZE;
> > > u32 sectors = 0;
> > > sense_reason_t ret;
> > >
> > > @@ -1212,7 +1213,7 @@ sbc_parse_cdb(struct se_cmd *cmd, struct sbc_ops *ops)
> > > return TCM_ADDRESS_OUT_OF_RANGE;
> > > }
> > >
> > > - if (!(cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE))
> > > + if (size == INVALID_SIZE)
> > > size = sbc_get_size(cmd, sectors);
> > > }
> > >
> >
> > This patch has no effect.
>
> Hello Nic,
>
> That's a misinterpretation of your side. What this patch does is to ensure
> that 'size' remains zero if a VERIFY or WRITE AND VERIFY command is submitted
> with BYTCHK == 0. SBC mentions clearly that BYTCHK == 0 means that there is
> no Data-Out buffer, or in other words, that the size of the Data-Out buffer
> is zero.
>
> From the sg_verify man page:
>
> When --ndo=NDO is not given then the verify starts at the logical block
> address given by the --lba=LBA option and continues for --count=COUNT
> blocks.
>
> In other words, sg_verify is able to submit a VERIFY command without Data-Out
> buffer (NDO is the size of the Data-Out buffer in bytes).
>
That's fine the spec says no data is associated with bytchk = 0.
The point is the 'size' value in sbc_parse_cdb() is what's extracted
from the received CDB, and compared against extended data transfer
length (cmd->data_length) in target_cmd_size_check() to determine
overflow or underflow.
Attempting to make 'size' in sbc_parse_cdb() enforce what the spec says,
instead of what it actually is in the received CDB is completely wrong.
No other CDB does this, and *VERIFY* is no exception.
If you're worried about non zero transfer length with bytchk = 0 getting
processed, go ahead and return TCM_INVALID_CDB_FIELD from
sbc_parse_verify() when this happens, like every other sanity check
does.
Of course, that's exactly the test case libiscsi does during
test_writeverify16_residuals, send bythck = 0 with overflow and
underflow with a non zero transfer length.
> > Anyways, I've fixed both cases and will post the proper fix inline
> > against patch #19.
>
> Do you perhaps mean patch "target: Fix sbc_parse_verify bytchk = 0 handling"?
> (https://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending.git/commit/?h=for-next&id=d7d40280f868463d01a82186fd61cdc0e590381f)
>
> If you want to know my opinion about that patch: it doesn't fix anything but
> breaks the sbc_parse_verify() function and definitely doesn't make the
> behavior of VERIFY nor WRITE AND VERIFY more compliant with the SCSI specs.
You are incorrect.
It addresses the regression your code introduced that broke existing
behavior for WRITE_VERIFY_*, when sbc_parse_verify() dropped
SCF_SCSI_DATA_CDB for bytchk = 0 that allowed overflow to trigger an
NULL pointer dereference.
Perhaps you should verify existing code before your sbc_parse_verify()
changes to see what I'm talking about.
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