sunrpc: don't mark uninitialised items as VALID.

A recent commit added a call to cache_fresh_locked()
when an expired item was found.
The call sets the CACHE_VALID flag, so it is important
that the item actually is valid.
There are two ways it could be valid:
1/ If ->update has been called to fill in relevant content
2/ if CACHE_NEGATIVE is set, to say that content doesn't exist.

An expired item that is waiting for an update will be neither.
Setting CACHE_VALID will mean that a subsequent call to cache_put()
will be likely to dereference uninitialised pointers.

So we must make sure the item is valid, and we already have code to do
that in try_to_negate_entry().  This takes the hash lock and so cannot
be used directly, so take out the two lines that we need and use them.

Now cache_fresh_locked() is certain to be called only on
a valid item.

Cc: stable@kernel.org # 2.6.35
Fixes: 4ecd55ea0742 ("sunrpc: fix cache_head leak due to queued request")
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 12bb23b8e0c50c80abd51c69a5c5a2ea6433a723..261131dfa1f1ba3900d85088a6cfde659bbe231a 100644 (file)
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -54,6 +54,7 @@ static void cache_init(struct cache_head *h, struct cache_detail *detail)
        h->last_refresh = now;
 }
 
+static inline int cache_is_valid(struct cache_head *h);
 static void cache_fresh_locked(struct cache_head *head, time_t expiry,
                                struct cache_detail *detail);
 static void cache_fresh_unlocked(struct cache_head *head,
@@ -105,6 +106,8 @@ static struct cache_head *sunrpc_cache_add_entry(struct cache_detail *detail,
                        if (cache_is_expired(detail, tmp)) {
                                hlist_del_init_rcu(&tmp->cache_list);
                                detail->entries --;
+                               if (cache_is_valid(tmp) == -EAGAIN)
+                                       set_bit(CACHE_NEGATIVE, &tmp->flags);
                                cache_fresh_locked(tmp, 0, detail);
                                freeme = tmp;
                                break;