From: Xie He xie.he.0141@gmail.com
[ Upstream commit 88c7a9fd9bdd3e453f04018920964c6f848a591a ]
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.
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") Signed-off-by: Xie He xie.he.0141@gmail.com Acked-by: Martin Schiller ms@dev.tdt.de Link: https://lore.kernel.org/r/20210201055706.415842-1-xie.he.0141@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 ba4d015bd1a67..7cbb77b7479a6 100644 --- a/net/lapb/lapb_out.c +++ b/net/lapb/lapb_out.c @@ -87,7 +87,8 @@ 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; }