On Fri, Apr 05 2019, NeilBrown wrote:
>
> Unfortunately I was wrong. See below.
>
Arrghh.. Ignore that patch. Use this one.
NeilBrown
From b7a8dced1a34869710a5d68a64e8bd37bf2ab426 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@xxxxxxxx>
Date: Fri, 5 Apr 2019 09:04:41 +1100
Subject: [PATCH] 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@xxxxxxxxxx # 2.6.35
Fixes: 4ecd55ea0742 ("sunrpc: fix cache_head leak due to queued request")
Signed-off-by: NeilBrown <neilb@xxxxxxxx>
---
net/sunrpc/cache.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 12bb23b8e0c5..261131dfa1f1 100644
--- 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;
--
2.14.0.rc0.dirty
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