linux-kernel - [PATCH net] net/xen-netback: prevent UAF in xenvif_flush

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Message-Id: <20240822181109.2577354-1-aha310510@gmail.com>
Date: Fri, 23 Aug 2024 03:11:09 +0900
From: Jeongjun Park <aha310510@...il.com>
To: wei.liu@...nel.org,
	paul@....org
Cc: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	madhuparnabhowmik04@...il.com,
	xen-devel@...ts.xenproject.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jeongjun Park <aha310510@...il.com>
Subject: [PATCH net] net/xen-netback: prevent UAF in xenvif_flush_hash()

During the list_for_each_entry_rcu iteration call of xenvif_flush_hash, 
kfree_rcu does not exist inside the rcu read critical section, so if 
kfree_rcu is called when the rcu grace period ends during the iteration, 
UAF occurs when accessing head->next after the entry becomes free.

Therefore, to solve this, you need to change it to list_for_each_entry_safe.

Fixes: f3265971ded9 ("net: xen-netback: hash.c: Use built-in RCU list checking")
Signed-off-by: Jeongjun Park <aha310510@...il.com>
---
 drivers/net/xen-netback/hash.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/net/xen-netback/hash.c b/drivers/net/xen-netback/hash.c
index ff96f22648ef..45ddce35f6d2 100644
--- a/drivers/net/xen-netback/hash.c
+++ b/drivers/net/xen-netback/hash.c
@@ -95,7 +95,7 @@ static u32 xenvif_new_hash(struct xenvif *vif, const u8 *data,
 
 static void xenvif_flush_hash(struct xenvif *vif)
 {
-	struct xenvif_hash_cache_entry *entry;
+	struct xenvif_hash_cache_entry *entry, *n;
 	unsigned long flags;
 
 	if (xenvif_hash_cache_size == 0)
@@ -103,8 +103,7 @@ static void xenvif_flush_hash(struct xenvif *vif)
 
 	spin_lock_irqsave(&vif->hash.cache.lock, flags);
 
-	list_for_each_entry_rcu(entry, &vif->hash.cache.list, link,
-				lockdep_is_held(&vif->hash.cache.lock)) {
+	list_for_each_entry_safe(entry, n, &vif->hash.cache.list, link) {
 		list_del_rcu(&entry->link);
 		vif->hash.cache.count--;
 		kfree_rcu(entry, rcu);
--