[v5,1/4] hash: fix race condition in iterate

  In rte_hash_iterate, the reader lock did not protect the
while loop which checks empty entry. This created a race
condition that the entry may become empty when enters
the lock, then a wrong key data value would be read out.

This commit reads out the position in the while condition,
which makes sure that the position will not be changed
to empty before entering the lock.

Fixes: f2e3001b53ec ("hash: support read/write concurrency")
Cc: stable@dpdk.org

Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
Reported-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
---
 lib/librte_hash/rte_cuckoo_hash.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)
  

> -----Original Message-----
> From: Yipeng Wang <yipeng1.wang@intel.com>
> Sent: Monday, October 1, 2018 1:35 PM
> To: bruce.richardson@intel.com
> Cc: konstantin.ananyev@intel.com; dev@dpdk.org;
> yipeng1.wang@intel.com; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; sameh.gobriel@intel.com
> Subject: [PATCH v5 1/4] hash: fix race condition in iterate
> 
> In rte_hash_iterate, the reader lock did not protect the while loop which
> checks empty entry. This created a race condition that the entry may
> become empty when enters the lock, then a wrong key data value would be
> read out.
> 
> This commit reads out the position in the while condition, which makes sure
> that the position will not be changed to empty before entering the lock.
> 
> Fixes: f2e3001b53ec ("hash: support read/write concurrency")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
> Reported-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> ---
>  lib/librte_hash/rte_cuckoo_hash.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/librte_hash/rte_cuckoo_hash.c
> b/lib/librte_hash/rte_cuckoo_hash.c
> index f7b86c8..da8ddf4 100644
> --- a/lib/librte_hash/rte_cuckoo_hash.c
> +++ b/lib/librte_hash/rte_cuckoo_hash.c
> @@ -1318,7 +1318,7 @@ rte_hash_iterate(const struct rte_hash *h, const
> void **key, void **data, uint32
>  	idx = *next % RTE_HASH_BUCKET_ENTRIES;
> 
>  	/* If current position is empty, go to the next one */
> -	while (h->buckets[bucket_idx].key_idx[idx] == EMPTY_SLOT) {
> +	while ((position = h->buckets[bucket_idx].key_idx[idx]) ==
> EMPTY_SLOT)
> +{
>  		(*next)++;
>  		/* End of table */
>  		if (*next == total_entries)
> @@ -1326,9 +1326,8 @@ rte_hash_iterate(const struct rte_hash *h, const
> void **key, void **data, uint32
>  		bucket_idx = *next / RTE_HASH_BUCKET_ENTRIES;
>  		idx = *next % RTE_HASH_BUCKET_ENTRIES;
>  	}
> +
>  	__hash_rw_reader_lock(h);
> -	/* Get position of entry in key table */
> -	position = h->buckets[bucket_idx].key_idx[idx];
>  	next_key = (struct rte_hash_key *) ((char *)h->key_store +
>  				position * h->key_entry_size);
>  	/* Return key and data */
> --
> 2.7.4
This looks good. I can rework my patch too. I will leave the decision to you.

Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>