GTPv1-U packets may carry a chain of extension headers before the inner IP packet. The receive path already parses and skips these extension headers, but it currently reads the inner protocol before doing so.

As a result, the first extension header byte is interpreted as the inner IP version. Packets with extension headers are then dropped before PDP lookup.

Parse the extension header chain before calling gtp_inner_proto(), so the inner protocol is read from the actual inner IP header.

Fixes: c75fc0b9e5be ("gtp: identify tunnel via GTP device + GTP version + TEID + family") Signed-off-by: Zhixing Chen running910@gmail.com ---

Changes in v3: - Refetch the GTP header after pskb_may_pull() before checking the extension-header flag.

Changes in v2: - Add missing Fixes tag.

v2: https://lore.kernel.org/netdev/20260703093708.18141-1-running910@gmail.com/T... v1: https://lore.kernel.org/netdev/20260703084244.59077-1-running910@gmail.com/T...

--- drivers/net/gtp.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c index a60ef32b35b8..c0e38878af51 100644 --- a/drivers/net/gtp.c +++ b/drivers/net/gtp.c @@ -826,13 +826,17 @@ static int gtp1u_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb) if (!pskb_may_pull(skb, hdrlen)) return -1;

+ gtp1 = (struct gtp1_header *)(skb->data + sizeof(struct udphdr)); + + if (gtp1->flags & GTP1_F_EXTHDR && + gtp_parse_exthdrs(skb, &hdrlen) < 0) + return -1; + if (gtp_inner_proto(skb, hdrlen, &inner_proto) < 0) { netdev_dbg(gtp->dev, "GTP packet does not encapsulate an IP packet\n"); return -1; }

- gtp1 = (struct gtp1_header *)(skb->data + sizeof(struct udphdr)); - pctx = gtp1_pdp_find(gtp, ntohl(gtp1->tid), gtp_proto_to_family(inner_proto)); if (!pctx) { @@ -840,10 +844,6 @@ static int gtp1u_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb) return 1; }

- if (gtp1->flags & GTP1_F_EXTHDR && - gtp_parse_exthdrs(skb, &hdrlen) < 0) - return -1; - return gtp_rx(pctx, skb, hdrlen, gtp->role, inner_proto); }