From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933781AbbIDNk2 (ORCPT ); Fri, 4 Sep 2015 09:40:28 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:50126 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932927AbbIDNJo (ORCPT ); Fri, 4 Sep 2015 09:09:44 -0400 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Herbert Xu , "David S. Miller" , Luis Henriques Subject: [PATCH 3.16.y-ckt 068/130] net: Clone skb before setting peeked flag Date: Fri, 4 Sep 2015 14:07:36 +0100 Message-Id: <1441372118-5933-69-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1441372118-5933-1-git-send-email-luis.henriques@canonical.com> References: <1441372118-5933-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.16 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.7-ckt17 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Herbert Xu 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 Signed-off-by: Luis Henriques --- 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 488dd1a825c0..4e07eaef9949 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -130,6 +130,35 @@ 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 @@ -164,7 +193,9 @@ out_noerr: struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags, int *peeked, int *off, int *err) { + struct sk_buff_head *queue = &sk->sk_receive_queue; struct sk_buff *skb, *last; + unsigned long cpu_flags; long timeo; /* * Caller is allowed not to check sk->sk_err before skb_recv_datagram() @@ -183,8 +214,6 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int 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; int _off = *off; last = (struct sk_buff *)queue; @@ -198,7 +227,11 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int 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); @@ -222,6 +255,8 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags, return NULL; +unlock_err: + spin_unlock_irqrestore(&queue->lock, cpu_flags); no_packet: *err = error; return NULL;