Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966124AbcCPII4 (ORCPT ); Wed, 16 Mar 2016 04:08:56 -0400 Received: from mail.kernel.org ([198.145.29.136]:59467 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965070AbcCPIIq (ORCPT ); Wed, 16 Mar 2016 04:08:46 -0400 From: lizf@kernel.org To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Herbert Xu , "David S. Miller" , Zefan Li Subject: [PATCH 3.4 029/107] net: Clone skb before setting peeked flag Date: Wed, 16 Mar 2016 16:05:23 +0800 Message-Id: <1458115601-5762-29-git-send-email-lizf@kernel.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1458115541-5712-1-git-send-email-lizf@kernel.org> References: <1458115541-5712-1-git-send-email-lizf@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3033 Lines: 113 From: Herbert Xu 3.4.111-rc1 review patch. If anyone has any objections, please let me know. ------------------ commit 738ac1ebb96d02e0d23bc320302a6ea94c612dec upstream. Shared skbs must not be modified and this is crucial for broadcast and/or multicast paths where we use it as an optimisation to avoid unnecessary cloning. The function skb_recv_datagram breaks this rule by setting peeked without cloning the skb first. This causes funky races which leads to double-free. This patch fixes this by cloning the skb and replacing the skb in the list when setting skb->peeked. Fixes: a59322be07c9 ("[UDP]: Only increment counter on first peek/recv") Reported-by: Konstantin Khlebnikov Signed-off-by: Herbert Xu Signed-off-by: David S. Miller [lizf: Backported to 3.4: adjust context] Signed-off-by: Zefan Li --- net/core/datagram.c | 41 ++++++++++++++++++++++++++++++++++++++--- 1 file changed, 38 insertions(+), 3 deletions(-) diff --git a/net/core/datagram.c b/net/core/datagram.c index da7e0c8..ba96ad9 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -127,6 +127,35 @@ out_noerr: goto out; } +static int skb_set_peeked(struct sk_buff *skb) +{ + struct sk_buff *nskb; + + if (skb->peeked) + return 0; + + /* We have to unshare an skb before modifying it. */ + if (!skb_shared(skb)) + goto done; + + nskb = skb_clone(skb, GFP_ATOMIC); + if (!nskb) + return -ENOMEM; + + skb->prev->next = nskb; + skb->next->prev = nskb; + nskb->prev = skb->prev; + nskb->next = skb->next; + + consume_skb(skb); + skb = nskb; + +done: + skb->peeked = 1; + + return 0; +} + /** * __skb_recv_datagram - Receive a datagram skbuff * @sk: socket @@ -161,7 +190,9 @@ out_noerr: struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags, int *peeked, int *off, int *err) { + struct sk_buff_head *queue = &sk->sk_receive_queue; struct sk_buff *skb; + unsigned long cpu_flags; long timeo; /* * Caller is allowed not to check sk->sk_err before skb_recv_datagram() @@ -180,8 +211,6 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags, * Look at current nfs client by the way... * However, this function was correct in any case. 8) */ - unsigned long cpu_flags; - struct sk_buff_head *queue = &sk->sk_receive_queue; spin_lock_irqsave(&queue->lock, cpu_flags); skb_queue_walk(queue, skb) { @@ -191,7 +220,11 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags, *off -= skb->len; continue; } - skb->peeked = 1; + + error = skb_set_peeked(skb); + if (error) + goto unlock_err; + atomic_inc(&skb->users); } else __skb_unlink(skb, queue); @@ -210,6 +243,8 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags, return NULL; +unlock_err: + spin_unlock_irqrestore(&queue->lock, cpu_flags); no_packet: *err = error; return NULL; -- 1.9.1