[3.19.y-ckt stable] Patch "inet: frag: don't re-use chainlist for evictor" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    inet: frag: don't re-use chainlist for evictor

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt6.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From aa9fda1bb2ef65f334099c3b950d11fcc547c9d8 Mon Sep 17 00:00:00 2001
From: Florian Westphal <fw at strlen.de>
Date: Thu, 23 Jul 2015 12:05:37 +0200
Subject: inet: frag: don't re-use chainlist for evictor

commit d1fe19444d82e399e38c1594c71b850eca8e9de0 upstream.

commit 65ba1f1ec0eff ("inet: frags: fix a race between inet_evict_bucket
and inet_frag_kill") describes the bug, but the fix doesn't work reliably.

Problem is that ->flags member can be set on other cpu without chainlock
being held by that task, i.e. the RMW-Cycle can clear INET_FRAG_EVICTED
bit after we put the element on the evictor private list.

We can crash when walking the 'private' evictor list since an element can
be deleted from list underneath the evictor.

Join work with Nikolay Alexandrov.

Fixes: b13d3cbfb8e8 ("inet: frag: move eviction of queues to work queue")
Reported-by: Johan Schuijt <johan at transip.nl>
Tested-by: Frank Schreuder <fschreuder at transip.nl>
Signed-off-by: Nikolay Alexandrov <nikolay at cumulusnetworks.com>
Signed-off-by: Florian Westphal <fw at strlen.de>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 include/net/inet_frag.h  | 2 ++
 net/ipv4/inet_fragment.c | 8 +++-----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index 8d17655..3242bfd 100644
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -45,6 +45,7 @@ enum {
  * @flags: fragment queue flags
  * @max_size: (ipv4 only) maximum received fragment size with IP_DF set
  * @net: namespace that this frag belongs to
+ * @list_evictor: list of queues to forcefully evict (e.g. due to low memory)
  */
 struct inet_frag_queue {
 	spinlock_t		lock;
@@ -59,6 +60,7 @@ struct inet_frag_queue {
 	__u8			flags;
 	u16			max_size;
 	struct netns_frags	*net;
+	struct hlist_node	list_evictor;
 };

 #define INETFRAGS_HASHSZ	1024
diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index e792035..edc17b9 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -151,14 +151,13 @@ evict_again:
 		}

 		fq->flags |= INET_FRAG_EVICTED;
-		hlist_del(&fq->list);
-		hlist_add_head(&fq->list, &expired);
+		hlist_add_head(&fq->list_evictor, &expired);
 		++evicted;
 	}

 	spin_unlock(&hb->chain_lock);

-	hlist_for_each_entry_safe(fq, n, &expired, list)
+	hlist_for_each_entry_safe(fq, n, &expired, list_evictor)
 		f->frag_expire((unsigned long) fq);

 	return evicted;
@@ -284,8 +283,7 @@ static inline void fq_unlink(struct inet_frag_queue *fq, struct inet_frags *f)
 	struct inet_frag_bucket *hb;

 	hb = get_frag_bucket_locked(fq, f);
-	if (!(fq->flags & INET_FRAG_EVICTED))
-		hlist_del(&fq->list);
+	hlist_del(&fq->list);
 	spin_unlock(&hb->chain_lock);
 }

--
1.9.1