Re: [PATCH] scsi: cxgb4i: potential array overflow in t4_uld_rx_handler()

[Varun Prakash <varun@chelsio.com>]

On Wed, Mar 28, 2018 at 08:30:37PM +0300, Dan Carpenter wrote:
> On Wed, Mar 28, 2018 at 09:14:25PM +0530, Varun Prakash wrote:
> > On Wed, Mar 21, 2018 at 09:12:00PM -0400, Martin K. Petersen wrote:
> > > 

> > > >
> > > > On Wed, Nov 29, 2017 at 02:42:20PM +0300, Dan Carpenter wrote:
> > > >> The story is that Smatch marks skb->data as untrusted and so it
> > > >> complains about this code:
> > > >> 
> > > >> 	drivers/scsi/cxgbi/cxgb4i/cxgb4i.c:2111 t4_uld_rx_handler()
> > > >> 	error: buffer overflow 'cxgb4i_cplhandlers' 239 <= 255.
> > > >> 
> > > >> I don't know the code very well, but it looks like a reasonable warning
> > > >> message.  Let's address it by adding a sanity check to make sure "opc"
> > > >> is within bounds.
> > > >> 
> > > >> Fixes: bbc02c7e9d34 ("cxgb4: Add register, message, and FW definitions")
> > > >> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > > >> 
> > > >> diff --git a/drivers/scsi/cxgbi/cxgb4i/cxgb4i.c b/drivers/scsi/cxgbi/cxgb4i/cxgb4i.c
> > > >> index 266eddf17a99..94b2d5660a07 100644
> > > >> --- a/drivers/scsi/cxgbi/cxgb4i/cxgb4i.c
> > > >> +++ b/drivers/scsi/cxgbi/cxgb4i/cxgb4i.c
> > > >> @@ -2108,12 +2108,12 @@ static int t4_uld_rx_handler(void *handle, const __be64 *rsp,
> > > >>  	log_debug(1 << CXGBI_DBG_TOE,
> > > >>  		"cdev %p, opcode 0x%x(0x%x,0x%x), skb %p.\n",
> > > >>  		 cdev, opc, rpl->ot.opcode_tid, ntohl(rpl->ot.opcode_tid), skb);
> > > >> -	if (cxgb4i_cplhandlers[opc])
> > > >> -		cxgb4i_cplhandlers[opc](cdev, skb);
> > > >> -	else {
> > > >> +	if (opc >= ARRAY_SIZE(cxgb4i_cplhandlers) || !cxgb4i_cplhandlers[opc]) {
> > > >>  		pr_err("No handler for opcode 0x%x.\n", opc);
> > > >>  		__kfree_skb(skb);
> > > >> +		return 0;
> > > >>  	}
> > > >> +	cxgb4i_cplhandlers[opc](cdev, skb);
> > > >>  	return 0;
> > > >>  nomem:
> > > >>  	log_debug(1 << CXGBI_DBG_TOE, "OOM bailing out.\n");
> > > >
> > > >
> > 
> > This check is not necessary but we can add it to avoid warning.
> 
> Is the reason it's not necessary, because the skb->data comes from the
> firmware and we trust it?

Yes, opc is an opcode of a cpl cmd which is generated by hardware or firmware,
driver should never get opc >= ARRAY_SIZE(cxgb4i_cplhandler) or NUM_CPL_CMDS(239).

> The v5 declares the array as having 256
> elements which also solves this warning.  And cxgbit_uld_lro_rx_handler()
> has a bounds check.  So it seems pretty normal to prevent the array
> overflow by force as well as by trust.
> 
> > The commit mentioned in "Fixes" is not correct, this code was added in commit 
> > "7b36b6e [SCSI] cxgb4i v5: iscsi driver"
> 
> Yeah.  You're right.  I can resend with an updated commit message.
> 
> regards,
> dan carpenter
>