+CC Sasha Levin
FYI: this patch fixes race in netlink which leads to hung in glibc
function getaddrinfo() because it doesn't handle errors at all.
On 26.06.2015 13:48, Konstantin Khlebnikov wrote:
Hash value passed as argument into rhashtable_lookup_compare could be
computed using different hash table than rhashtable_lookup_compare sees.
This patch passes key into rhashtable_lookup_compare() instead of hash and
compures hash value right in place using the same table as for lookup.
Also it adds comment for rhashtable_hashfn and rhashtable_obj_hashfn:
user must prevent concurrent insert/remove otherwise returned hash value
could be invalid.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Fixes: e341694e3eb5 ("netlink: Convert netlink_lookup() to use RCU protected hash table")
Link: http://lkml.kernel.org/r/20150514042151.GA5482@xxxxxxxxxxxxxxxxxxx
Cc: Stable <stable@xxxxxxxxxxxxxxx> (v3.17 .. v3.19)
---
include/linux/rhashtable.h | 2 +-
lib/rhashtable.c | 12 ++++++++----
net/netlink/af_netlink.c | 5 +----
3 files changed, 10 insertions(+), 9 deletions(-)
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index fb298e9d6d3a..84056743780a 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -108,7 +108,7 @@ int rhashtable_expand(struct rhashtable *ht, gfp_t flags);
int rhashtable_shrink(struct rhashtable *ht, gfp_t flags);
void *rhashtable_lookup(const struct rhashtable *ht, const void *key);
-void *rhashtable_lookup_compare(const struct rhashtable *ht, u32 hash,
+void *rhashtable_lookup_compare(const struct rhashtable *ht, void *key,
bool (*compare)(void *, void *), void *arg);
void rhashtable_destroy(const struct rhashtable *ht);
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 624a0b7c05ef..cb22073fe687 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -61,6 +61,8 @@ static u32 __hashfn(const struct rhashtable *ht, const void *key,
* Computes the hash value using the hash function provided in the 'hashfn'
* of struct rhashtable_params. The returned value is guaranteed to be
* smaller than the number of buckets in the hash table.
+ *
+ * The caller must ensure that no concurrent table mutations occur.
*/
u32 rhashtable_hashfn(const struct rhashtable *ht, const void *key, u32 len)
{
@@ -92,6 +94,8 @@ static u32 obj_hashfn(const struct rhashtable *ht, const void *ptr, u32 hsize)
* 'obj_hashfn' depending on whether the hash table is set up to work with
* a fixed length key. The returned value is guaranteed to be smaller than
* the number of buckets in the hash table.
+ *
+ * The caller must ensure that no concurrent table mutations occur.
*/
u32 rhashtable_obj_hashfn(const struct rhashtable *ht, void *ptr)
{
@@ -474,7 +478,7 @@ EXPORT_SYMBOL_GPL(rhashtable_lookup);
/**
* rhashtable_lookup_compare - search hash table with compare function
* @ht: hash table
- * @hash: hash value of desired entry
+ * @key: pointer to key
* @compare: compare function, must return true on match
* @arg: argument passed on to compare function
*
@@ -486,14 +490,14 @@ EXPORT_SYMBOL_GPL(rhashtable_lookup);
*
* Returns the first entry on which the compare function returned true.
*/
-void *rhashtable_lookup_compare(const struct rhashtable *ht, u32 hash,
+void *rhashtable_lookup_compare(const struct rhashtable *ht, void *key,
bool (*compare)(void *, void *), void *arg)
{
const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
struct rhash_head *he;
+ u32 hash;
- if (unlikely(hash >= tbl->size))
- return NULL;
+ hash = __hashfn(ht, key, ht->p.key_len, tbl->size);
rht_for_each_rcu(he, tbl->buckets[hash], ht) {
if (!compare(rht_obj(ht, he), arg))
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index c0a418766f9c..c82b2e37e652 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1003,11 +1003,8 @@ static struct sock *__netlink_lookup(struct netlink_table *table, u32 portid,
.net = net,
.portid = portid,
};
- u32 hash;
- hash = rhashtable_hashfn(&table->hash, &portid, sizeof(portid));
-
- return rhashtable_lookup_compare(&table->hash, hash,
+ return rhashtable_lookup_compare(&table->hash, &portid,
&netlink_compare, &arg);
}
--
Konstantin
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