Re: [PATCH 0/1] cache_head leak in sunrpc_cache_lookup()

[NeilBrown <neilb@suse.com>]

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