[PATCH net] net/xen-netback: prevent UAF in xenvif_flush_hash()

[Jeongjun Park <aha310510@xxxxxxxxx>]

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@xxxxxxxxx>
---
 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);
--