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Miller" , Jakub Kicinski , Paolo Abeni Cc: Andrew Lunn , Simon Horman , netdev@vger.kernel.org, eric.dumazet@gmail.com, Eric Dumazet , Mitchell Blank Jr , Chas Williams <3chas3@gmail.com>, Qingfang Deng Content-Type: text/plain; charset="UTF-8" In pppoatm_send(), LLC encapsulation checks whether there is sufficient headroom for the 4-byte LLC header, but does not ensure that the skb header is writable. Normal transmit packets passing through ppp_start_xmit() have their header unshared via skb_cow_head(). However, packets can also reach pppoatm_send() via PPP channel bridging (PPPIOCBRIDGECHAN) without going through ppp_start_xmit(). Use skb_cow_head() to ensure both sufficient headroom and a writable header before pushing the LLC header. While at it, this also simplifies the code and avoids allocating and freeing a temporary skb when the ATM socket buffer is full. Fixes: 4cf476ced45d ("ppp: add PPPIOCBRIDGECHAN and PPPIOCUNBRIDGECHAN ioctls") Signed-off-by: Eric Dumazet --- Cc: Mitchell Blank Jr Cc: Chas Williams <3chas3@gmail.com> Cc: Qingfang Deng --- net/atm/pppoatm.c | 21 ++++++--------------- 1 file changed, 6 insertions(+), 15 deletions(-) diff --git a/net/atm/pppoatm.c b/net/atm/pppoatm.c index 6da52d12df68e493b03f57edc46c3b5255956893..4ce7fa6e493e95d64909b72fd123a517c0befb12 100644 --- a/net/atm/pppoatm.c +++ b/net/atm/pppoatm.c @@ -317,21 +317,12 @@ static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb) switch (pvcc->encaps) { /* LLC encapsulation needed */ case e_llc: - if (skb_headroom(skb) < LLC_LEN) { - struct sk_buff *n; - n = skb_realloc_headroom(skb, LLC_LEN); - if (n != NULL && - !pppoatm_may_send(pvcc, n->truesize)) { - kfree_skb(n); - goto nospace; - } - consume_skb(skb); - skb = n; - if (skb == NULL) { - bh_unlock_sock(sk_atm(vcc)); - return DROP_PACKET; - } - } else if (!pppoatm_may_send(pvcc, skb->truesize)) + if (skb_cow_head(skb, LLC_LEN)) { + bh_unlock_sock(sk_atm(vcc)); + kfree_skb(skb); + return DROP_PACKET; + } + if (!pppoatm_may_send(pvcc, skb->truesize)) goto nospace; memcpy(skb_push(skb, LLC_LEN), pppllc, LLC_LEN); break; -- 2.55.0.979.g7e5102b832-goog