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Date: Mon, 1 Feb 2021 15:10:45 +0100 From: Julian Wiedmann <jwi@...ux.ibm.com> To: Xie He <xie.he.0141@...il.com>, "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, linux-x25@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Martin Schiller <ms@....tdt.de> Subject: Re: [PATCH net] net: lapb: Copy the skb before sending a packet On 01.02.21 06:57, Xie He wrote: > When sending a packet, we will prepend it with an LAPB header. > This modifies the shared parts of a cloned skb, so we should copy the > skb rather than just clone it, before we prepend the header. > > In "Documentation/networking/driver.rst" (the 2nd point), it states > that drivers shouldn't modify the shared parts of a cloned skb when > transmitting. > This sounds a bit like you want skb_cow_head() ... ? > The "dev_queue_xmit_nit" function in "net/core/dev.c", which is called > when an skb is being sent, clones the skb and sents the clone to > AF_PACKET sockets. Because the LAPB drivers first remove a 1-byte > pseudo-header before handing over the skb to us, if we don't copy the > skb before prepending the LAPB header, the first byte of the packets > received on AF_PACKET sockets can be corrupted. > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Cc: Martin Schiller <ms@....tdt.de> > Signed-off-by: Xie He <xie.he.0141@...il.com> > --- > net/lapb/lapb_out.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/net/lapb/lapb_out.c b/net/lapb/lapb_out.c > index 7a4d0715d1c3..a966d29c772d 100644 > --- a/net/lapb/lapb_out.c > +++ b/net/lapb/lapb_out.c > @@ -82,7 +82,8 @@ void lapb_kick(struct lapb_cb *lapb) > skb = skb_dequeue(&lapb->write_queue); > > do { > - if ((skbn = skb_clone(skb, GFP_ATOMIC)) == NULL) { > + skbn = skb_copy(skb, GFP_ATOMIC); > + if (!skbn) { > skb_queue_head(&lapb->write_queue, skb); > break; > } >
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