Re: [dpdk-dev] [PATCH] net/softnic: fix illegal memory access

["Singh, Jasvinder" <jasvinder.singh@intel.com>]

> -----Original Message-----
> From: Dumitrescu, Cristian
> Sent: Monday, July 16, 2018 5:04 PM
> To: Singh, Jasvinder <jasvinder.singh@intel.com>; dev@dpdk.org
> Subject: RE: [PATCH] net/softnic: fix illegal memory access
> 
> 
> 
> > -----Original Message-----
> > From: Singh, Jasvinder
> > Sent: Monday, July 16, 2018 1:42 PM
> > To: dev@dpdk.org
> > Cc: Dumitrescu, Cristian <cristian.dumitrescu@intel.com>
> > Subject: [PATCH] net/softnic: fix illegal memory access
> >
> > Fix pointer dereferencing and read after free (USE_AFTER_FREE).
> >
> > Coverity issue: 302867
> > Fixes: bef50bcb1c47 ("net/softnic: implement start and stop")
> >
> > Signed-off-by: Jasvinder Singh <jasvinder.singh@intel.com>
> > ---
> >  drivers/net/softnic/rte_eth_softnic_swq.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/softnic/rte_eth_softnic_swq.c
> > b/drivers/net/softnic/rte_eth_softnic_swq.c
> > index 1944fbb..604a2cc 100644
> > --- a/drivers/net/softnic/rte_eth_softnic_swq.c
> > +++ b/drivers/net/softnic/rte_eth_softnic_swq.c
> > @@ -36,9 +36,13 @@ softnic_swq_free(struct pmd_internals *p)  void
> > softnic_softnic_swq_free_keep_rxq_txq(struct pmd_internals *p)  {
> > -	struct softnic_swq *swq;
> > +	for ( ; ; ) {
> > +		struct softnic_swq *swq;
> > +
> > +		swq = TAILQ_FIRST(&p->swq_list);
> > +		if (swq == NULL)
> > +			break;
> >
> > -	TAILQ_FOREACH(swq, &p->swq_list, node) {
> >  		if ((strncmp(swq->name, "RXQ", strlen("RXQ")) == 0) ||
> >  			(strncmp(swq->name, "TXQ", strlen("TXQ")) == 0))
> >  			continue;
> > --
> > 2.9.3
> 
> Where is the bug? We simply parse a linked list to free each element.

Below is coverity log on the issue;   
 
void
 softnic_softnic_swq_free_keep_rxq_txq(struct pmd_internals *p)
 {
         struct softnic_swq *swq;
    	1. Condition swq, taking true branch.
   	4. Condition swq, taking true branch.
   	7. alias: Assigning: swq = swq->node.tqe_next. Now both point to the same storage.
   	8. Condition swq, taking true branch.
   	
CID 302867 (#1-2 of 2): Read from pointer after free (USE_AFTER_FREE)
15. deref_after_free: Dereferencing freed pointer swq.
         TAILQ_FOREACH(swq, &p->swq_list, node) {
   	2. Condition strncmp(swq->name, "RXQ", strlen("RXQ")) == 0, taking true branch.
   	5. Condition strncmp(swq->name, "RXQ", strlen("RXQ")) == 0, taking true branch.
   	9. Condition strncmp(swq->name, "RXQ", strlen("RXQ")) == 0, taking false branch.
   	10. Condition strncmp(swq->name, "TXQ", strlen("TXQ")) == 0, taking false branch.
                 if ((strncmp(swq->name, "RXQ", strlen("RXQ")) == 0) ||
                         (strncmp(swq->name, "TXQ", strlen("TXQ")) == 0))
   	3. Continuing loop.
   	6. Continuing loop.
                         continue;
 
   	11. Condition swq->node.tqe_next != NULL, taking true branch.
   	12. Falling through to end of if statement.
                 TAILQ_REMOVE(&p->swq_list, swq, node);
                rte_ring_free(swq->r);
   	13. freed_arg: free frees swq.
                 free(swq);
   	14. Jumping back to the beginning of the loop.
         }
 }