[PATCH 3.16 073/157] sunrpc: don't mark uninitialised items as VALID.

[Ben Hutchings]

3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: NeilBrown <neilb@xxxxxxxx>

commit d58431eacb226222430940134d97bfd72f292fcd upstream.

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.

Fixes: 4ecd55ea0742 ("sunrpc: fix cache_head leak due to queued request")
Signed-off-by: NeilBrown <neilb@xxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/sunrpc/cache.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -50,6 +50,7 @@ static void cache_init(struct cache_head
 	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);
 static void cache_fresh_unlocked(struct cache_head *head,
 				struct cache_detail *detail);
@@ -98,6 +99,8 @@ struct cache_head *sunrpc_cache_lookup(s
 				*hp = tmp->next;
 				tmp->next = NULL;
 				detail->entries --;
+				if (cache_is_valid(tmp) == -EAGAIN)
+					set_bit(CACHE_NEGATIVE, &tmp->flags);
 				cache_fresh_locked(tmp, 0);
 				freeme = tmp;
 				break;