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Date: Wed, 30 Nov 2011 20:06:09 -0800 From: Tom Herbert <therbert@...gle.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Linux Netdev List <netdev@...r.kernel.org>, David Miller <davem@...emloft.net> Subject: Re: Bug in computing data_len in tcp_sendmsg? On Wed, Nov 30, 2011 at 7:42 PM, Eric Dumazet <eric.dumazet@...il.com> wrote: > Le mercredi 30 novembre 2011 à 17:48 -0800, Tom Herbert a écrit : >> I believe that skb->data_len might no be computed correctly in >> tcp_sendmsg. Specifically, when skb_add_data_nocache (or >> skb_add_data) is called skb->data_len is not updated (skb_put only >> updates skb->len). This results in the datalen in the head skbuf >> being zero so any subsequent uses of the value lead to incorrect >> results. For instance, skb_headlen returns the length of the head >> skbu data and not just that of the headers. If I'm reading this >> correctly, it's a pretty fundamental bug. >> >> I don't have a fix for this yet. >> >> Tom > > On which tree do you see a problem ? > > For example net-next seems fine to me : > > On net-next. Look at skb_add_data_nocache. This doesn't touch data_len, and really can't since skb_put wants skb linearized. Actually, I think I am misinterpreting the meaning of data_len, looks like it is intended to return the number of bytes in the page buffer area (comment on the function would be have been nice ;-) ). It would seem that e1000e driver might be misinterpreting it also: segs = skb_shinfo(skb)->gso_segs ? : 1; /* multiply data chunks by size of headers */ bytecount = ((segs - 1) * skb_headlen(skb)) + skb->len; So maybe the bug is that e1000e is misusing the function (and it looks like some other drivers would be too)?. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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