From bd0900e5eed6502b314402d36ec11f6d1a67de82 Mon Sep 17 00:00:00 2001 From: Herbert Xu Date: Mon, 13 Jul 2015 20:01:42 +0800 Subject: [PATCH] net: Fix skb csum races when peeking commit 89c22d8c3b278212eef6a8cc66b570bc840a6f5a upstream. When we calculate the checksum on the recv path, we store the result in the skb as an optimisation in case we need the checksum again down the line. This is in fact bogus for the MSG_PEEK case as this is done without any locking. So multiple threads can peek and then store the result to the same skb, potentially resulting in bogus skb states. This patch fixes this by only storing the result if the skb is not shared. This preserves the optimisations for the few cases where it can be done safely due to locking or other reasons, e.g., SIOCINQ. Signed-off-by: Herbert Xu Acked-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Luis Henriques --- net/core/datagram.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/net/core/datagram.c b/net/core/datagram.c index 4e07eaef9949..2b2ed1ae5b63 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -779,7 +779,8 @@ __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len) !skb->csum_complete_sw) netdev_rx_csum_fault(skb->dev); } - skb->csum_valid = !sum; + if (!skb_shared(skb)) + skb->csum_valid = !sum; return sum; } EXPORT_SYMBOL(__skb_checksum_complete_head); @@ -799,11 +800,13 @@ __sum16 __skb_checksum_complete(struct sk_buff *skb) netdev_rx_csum_fault(skb->dev); } - /* Save full packet checksum */ - skb->csum = csum; - skb->ip_summed = CHECKSUM_COMPLETE; - skb->csum_complete_sw = 1; - skb->csum_valid = !sum; + if (!skb_shared(skb)) { + /* Save full packet checksum */ + skb->csum = csum; + skb->ip_summed = CHECKSUM_COMPLETE; + skb->csum_complete_sw = 1; + skb->csum_valid = !sum; + } return sum; }