| Message ID | 1227536527-29713-11-git-send-email-ilpo.jarvinen@helsinki.fi |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: "Ilpo Järvinen" <ilpo.jarvinen@helsinki.fi> Date: Mon, 24 Nov 2008 16:22:07 +0200 > This caused me to get repeatably: > > tcpdump: pcap_loop: recvfrom: Bad address > > Happens occassionally when I tcpdump my for-looped test xfers: > while [ : ]; do echo -n "$(date '+%s.%N') "; ./sendfile; sleep 20; done > > Rest of the relevant commands: > ethtool -K eth0 tso off > tc qdisc add dev eth0 root netem drop 4% > tcpdump -n -s0 -i eth0 -w sacklog.all I'm applying this in any event. What could be happening is some bad clone handling elsewhere (AF_PACKET, for example) and thus for some reason libpcap reads stale data then performs a packet read using incorrect lengths and this leads to reading past the end of it's user buffer and we -EFAULT. Just capturing the -EFAULT'ing call arguments with strace would be enough to give some deeper clues. Do you have that? -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 844b8ab..57555a4 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -2018,13 +2018,10 @@ void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len) skb_split_no_header(skb, skb1, len, pos); } -/* Shifting from/to a cloned skb is a no-go. - * - * TODO: handle cloned skbs by using pskb_expand_head() - */ +/* Shifting from/to a cloned skb is a no-go. */ static int skb_prepare_for_shift(struct sk_buff *skb) { - return skb_cloned(skb); + return skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC); } /**
This caused me to get repeatably: tcpdump: pcap_loop: recvfrom: Bad address Happens occassionally when I tcpdump my for-looped test xfers: while [ : ]; do echo -n "$(date '+%s.%N') "; ./sendfile; sleep 20; done Rest of the relevant commands: ethtool -K eth0 tso off tc qdisc add dev eth0 root netem drop 4% tcpdump -n -s0 -i eth0 -w sacklog.all Running net-next under kvm, connection goes to the same host (basically just out of kvm). The connection itself works ok and data gets sent without corruption even with a large number of tests while tcpdump fails usually within less than 5 tests. Whether it only happens because of this change or not, I don't know for sure but it's the only thing with which I've seen that error. The non-cloned variant works w/o it for much longer time. I'm yet to debug where the error actually comes from. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> --- net/core/skbuff.c | 7 ++----- 1 files changed, 2 insertions(+), 5 deletions(-)