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

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Message-ID: <lsq.1565469607.504505883@decadent.org.uk>
Date:   Sat, 10 Aug 2019 21:40:07 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "J. Bruce Fields" <bfields@...hat.com>,
        "NeilBrown" <neilb@...e.com>
Subject: [PATCH 3.16 073/157] sunrpc: don't mark uninitialised items as VALID.

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

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

From: NeilBrown <neilb@...e.com>

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@...e.com>
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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;