Re: [PATCH v2 2/2] net: avoid infinite loop in mpls_gso_segment when mpls_hlen == 0
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: 2021-03-08 16:08:32
Also in:
lkml, virtualization
On Mon, Mar 8, 2021 at 5:32 AM Balazs Nemeth [off-list ref] wrote:
quoted hunk ↗ jump to hunk
A packet with skb_inner_network_header(skb) == skb_network_header(skb) and ETH_P_MPLS_UC will prevent mpls_gso_segment from pulling any headers from the packet. Subsequently, the call to skb_mac_gso_segment will again call mpls_gso_segment with the same packet leading to an infinite loop. Signed-off-by: Balazs Nemeth <redacted> --- net/mpls/mpls_gso.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/net/mpls/mpls_gso.c b/net/mpls/mpls_gso.c index b1690149b6fa..cc1b6457fc93 100644 --- a/net/mpls/mpls_gso.c +++ b/net/mpls/mpls_gso.c@@ -27,7 +27,7 @@ static struct sk_buff *mpls_gso_segment(struct sk_buff *skb, skb_reset_network_header(skb); mpls_hlen = skb_inner_network_header(skb) - skb_network_header(skb); - if (unlikely(!pskb_may_pull(skb, mpls_hlen))) + if (unlikely(!mpls_hlen || !pskb_may_pull(skb, mpls_hlen))) goto out;
Good cathc. Besides length zero, this can be more strict: a label is 4B, so mpls_hlen needs to be >= 4B. Perhaps even aligned to 4B, too, but not if there may be other encap on top. Unfortunately there is no struct or type definition that we can use a sizeof instead of open coding the raw constant.