[dpdk-dev] [PATCH] net/i40e: fix the security risk of wild pointer operation

[Zhao1, Wei]

HI, Xiaolong & guojia

> -----Original Message-----
> From: Ye, Xiaolong <xiaolong.ye at intel.com>
> Sent: Friday, May 15, 2020 3:28 PM
> To: Guo, Jia <jia.guo at intel.com>
> Cc: Zhao1, Wei <wei.zhao1 at intel.com>; dev at dpdk.org; stable at dpdk.org;
> Xing, Beilei <beilei.xing at intel.com>
> Subject: Re: [dpdk-dev] [PATCH] net/i40e: fix the security risk of wild pointer
> operation
> 
> On 05/15, Jeff Guo wrote:
> >hi, zhaowei
> >
> >On 5/12/2020 11:19 PM, Wei Zhao wrote:
> >> In i40e PMD code of function i40e_res_pool_free(), if valid_entry is
> >> freed by "rte_free(valid_entry);" in the following code:
> >>
> >> if (prev != NULL) {
> >>   ........................
> >>
> >>     if (insert == 1) {
> >>       LIST_REMOVE(valid_entry, next);
> >>       rte_free(valid_entry);
> >>      } else {
> >>       rte_free(valid_entry);
> >>       insert = 1;
> >>      }
> >>    }
> >>
> >> then the following code for pool update may still use the wild
> >> pointer
> >> "valid_entry":
> >>
> >> " pool->num_free += valid_entry->len;
> >>    pool->num_alloc -= valid_entry>len; "
> >> it seems to be a security bug, we should avoid this risk.
> >>
> >> Cc: stable at dpdk.org
> >> Fixes: 4861cde46116 ("i40e: new poll mode driver")
> >>
> >> Signed-off-by: Wei Zhao <wei.zhao1 at intel.com>
> >> ---
> >>   drivers/net/i40e/i40e_ethdev.c | 6 +++---
> >>   1 file changed, 3 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/net/i40e/i40e_ethdev.c
> >> b/drivers/net/i40e/i40e_ethdev.c index 749d85f54..7f8ea5309 100644
> >> --- a/drivers/net/i40e/i40e_ethdev.c
> >> +++ b/drivers/net/i40e/i40e_ethdev.c
> >> @@ -4973,6 +4973,9 @@ i40e_res_pool_free(struct i40e_res_pool_info
> *pool,
> >>   	}
> >>   	insert = 0;
> >> +	pool->num_free += valid_entry->len;
> >> +	pool->num_alloc -= valid_entry->len;
> >> +
> >
> >
> >Shouldn't the pool count update after the pool->free_list updated by
> >"LIST_INSERT_HEAD(&pool->free_list, valid_entry, next)"?
> >
> >If so, you could use a variable to restore  valid_entry->len at the
> >begin and use it update pool count and other place.
> 
> Either way works from function point of view, but I do agree with Jeff that uses
> local variable to store the valid_entry->len at the beginning, and then updates
> the pool->num_free/num_alloc at the end.
> 
> Also I think it needs to set valid_entry to NULL after free it, it can avoid wild
> pointer case like this, if there is dereference of this pointer after setting it to
> NULL, program would crash directly and we can solve it early.
> 
> Thanks,
> Xiaolong

We must update it after find the proper one in the pool->free_list at once,  if we use a local pointer to store it,
The proper entry may has been freed in the following code, and merge with other free resource prev or next.


> 
> >
> >
> >>   	/* Try to merge with next one*/
> >>   	if (next != NULL) {
> >>   		/* Merge with next one */
> >> @@ -5010,9 +5013,6 @@ i40e_res_pool_free(struct i40e_res_pool_info
> *pool,
> >>   			LIST_INSERT_HEAD(&pool->free_list, valid_entry, next);
> >>   	}
> >> -	pool->num_free += valid_entry->len;
> >> -	pool->num_alloc -= valid_entry->len;
> >> -
> >>   	return 0;
> >>   }