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From:   Lv Yunlong <lyl2019@mail.ustc.edu.cn>
To:     dhowells@redhat.com, davem@davemloft.net, kuba@kernel.org
Cc:     linux-afs@lists.infradead.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Subject: [PATCH] net/rxrpc: Fix a use after free in rxrpc_input_packet
Date:   Thu,  1 Apr 2021 02:35:45 -0700
Message-Id: <20210401093545.4055-1-lyl2019@mail.ustc.edu.cn>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

In the case RXRPC_PACKET_TYPE_DATA of rxrpc_input_packet, if
skb_unshare(skb,..) failed, it will free the skb and return NULL.
But if skb_unshare() return NULL, the freed skb will be used by
rxrpc_eaten_skb(skb,..).

I see that rxrpc_eaten_skb() is used to drop a ref of skb. As the skb
is already freed in skb_unshare() on error, my patch removes the
rxrpc_eaten_skb() to avoid the uaf.

Fixes: d0d5c0cd1e711 ("rxrpc: Use skb_unshare() rather than skb_cow_data()")
Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
---
 net/rxrpc/input.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index dc201363f2c4..9ba408064465 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -1281,10 +1281,8 @@ int rxrpc_input_packet(struct sock *udp_sk, struct sk_buff *skb)
 		 */
 		if (sp->hdr.securityIndex != 0) {
 			struct sk_buff *nskb = skb_unshare(skb, GFP_ATOMIC);
-			if (!nskb) {
-				rxrpc_eaten_skb(skb, rxrpc_skb_unshared_nomem);
+			if (!nskb)
 				goto out;
-			}
 
 			if (nskb != skb) {
 				rxrpc_eaten_skb(skb, rxrpc_skb_received);
-- 
2.25.1