linux-kernel - [PATCH 3.16 219/328] batman-adv: Prevent duplicated global TT entry

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Message-ID: <lsq.1544392233.837590172@decadent.org.uk>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Sven Eckelmann" <sven@...fation.org>,
        "Simon Wunderlich" <sw@...onwunderlich.de>
Subject: [PATCH 3.16 219/328] batman-adv: Prevent duplicated global TT entry

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

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

From: Sven Eckelmann <sven@...fation.org>

commit e7136e48ffdfb9f37b0820f619380485eb407361 upstream.

The function batadv_tt_global_orig_entry_add is responsible for adding new
tt_orig_list_entry to the orig_list. It first checks whether the entry
already is in the list or not. If it is, then the creation of a new entry
is aborted.

But the lock for the list is only held when the list is really modified.
This could lead to duplicated entries because another context could create
an entry with the same key between the check and the list manipulation.

The check and the manipulation of the list must therefore be in the same
locked code section.

Fixes: d657e621a0f5 ("batman-adv: add reference counting for type batadv_tt_orig_list_entry")
Signed-off-by: Sven Eckelmann <sven@...fation.org>
Signed-off-by: Simon Wunderlich <sw@...onwunderlich.de>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/batman-adv/translation-table.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/batman-adv/translation-table.c
+++ b/net/batman-adv/translation-table.c
@@ -1287,6 +1287,8 @@ batadv_tt_global_orig_entry_add(struct b
 {
 	struct batadv_tt_orig_list_entry *orig_entry;
 
+	spin_lock_bh(&tt_global->list_lock);
+
 	orig_entry = batadv_tt_global_orig_entry_find(tt_global, orig_node);
 	if (orig_entry) {
 		/* refresh the ttvn: the current value could be a bogus one that
@@ -1309,10 +1311,8 @@ batadv_tt_global_orig_entry_add(struct b
 	orig_entry->flags = flags;
 	atomic_set(&orig_entry->refcount, 2);
 
-	spin_lock_bh(&tt_global->list_lock);
 	hlist_add_head_rcu(&orig_entry->list,
 			   &tt_global->orig_list);
-	spin_unlock_bh(&tt_global->list_lock);
 	atomic_inc(&tt_global->orig_list_count);
 
 sync_flags:
@@ -1320,6 +1320,8 @@ sync_flags:
 out:
 	if (orig_entry)
 		batadv_tt_orig_list_entry_free_ref(orig_entry);
+
+	spin_unlock_bh(&tt_global->list_lock);
 }
 
 /**