[PATCH 6.1 276/609] pppoe: reload header pointer after dev_hard_header()

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Asim Viladi Oglu Manizada <[email protected]>

commit e9c238f6fe42fb1b4dba3a578277de32cb487937 upstream.

pppoe_sendmsg() saves a pointer to the PPPoE header before calling
dev_hard_header(). Device header callbacks are allowed to reallocate the
skb head, invalidating pointers into it.

This can happen when a send is blocked in copy_from_user() while the first
non-Ethernet port is added to an empty team device. The team's delegated
GRE header callback then expands the skb head. PPPoE subsequently writes
six bytes through the stale pointer into the freed head.

Reload the PPPoE header through the skb's network-header offset after
device header creation. pskb_expand_head() updates that offset when it
relocates the head.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: [email protected]
Signed-off-by: Asim Viladi Oglu Manizada <[email protected]>
Reviewed-by: Vadim Fedorenko <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/net/ppp/pppoe.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/net/ppp/pppoe.c
+++ b/drivers/net/ppp/pppoe.c
@@ -900,6 +900,7 @@ static int pppoe_sendmsg(struct socket *
 	dev_hard_header(skb, dev, ETH_P_PPP_SES,
 			po->pppoe_pa.remote, NULL, total_len);
 
+	ph = pppoe_hdr(skb);
 	memcpy(ph, &hdr, sizeof(struct pppoe_hdr));
 
 	ph->length = htons(total_len);