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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Justin Iurman Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Yuya Kusakabe X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=2816; i=yuya.kusakabe@gmail.com; h=from:subject:message-id; bh=uNlx2hpfeoxZRCqrhu5DYCSMd8YIQavLzVraY8D2lTM=; b=owEBbQKS/ZANAwAIASrX0XUqXRtNAcsmYgBqqwxIMgHFbdimLQQJXT6/bd4d8vpzcsOlWPi8G HuUoqGnYOGJAjMEAAEIAB0WIQTaB7usAfxNKMeqa6Yq19F1Kl0bTQUCaqsMSAAKCRAq19F1Kl0b TVHCEACZ9/UU3vbviZElkjvyFmQTHOERAOE/Q9pCAx7PtLa2zcyl4KtncBvLyZLNFL91mjVGS4X UuZQkxVcsxZ4KYZh5sCqYWSrs9/j9MjuMAiAWNcYdi2gJEIO9E02P5098MiM+7RnL66jGmUjxCj OxEciSNiawABlBH8S4iGyX1UVLPb/CEgHGBdajGIXDNRml3o+jXu4ETBuahtDFFStFz84T55Y8a 6igo9Mf0xN74Opk7uw2WvQsC3dZdA0UEsgjCzh9u8D77O/YB/7PLgdEiHlAkF07qrBbMuijAHUE eybsL9IrCdGQIFKwUJPD1idCi+kdd1xhHKqnrRh1vnaubjydWaw6snYQTlLk4aJepPCS6SjorZG DKUEkW4Sp+Ssne88fhU19yy7m1qGVTtxCJdI9U6sUffBsQ5+1Ht6yOeeJpY3h9xqDILFvwjqI75 sPjcrhFD0Er+jZNGIGS5sUG/aUov6MHJY26aBNE6heavfk+fe8j4iQv5WJRF+nlwywRyb4zMhq9 8Rx+q6nnbNvgfPqabncqKSLGqdtXHny9C/YrEXvex2NKuzB3RHrwTUJeRWetHdAKwJc7CLR6oAb 2a5NhbXgQYGpKr03D4vrW7oZB5fY5vYro1QNPPKX5EB7VC0Age9eYqPq7JGPbuvhkC99KWGcYwz 8+f87cxDWeGHzTw== X-Developer-Key: i=yuya.kusakabe@gmail.com; a=openpgp; fpr=DA07BBAC01FC4D28C7AA6BA62AD7D1752A5D1B4D __seg6_do_srh_inline(), __seg6_do_srh_encap() and seg6_do_srh_encap_red() all grow the headroom with skb_cow_head(), push the new headers into it, and then rebuild the mac header below them with skb_mac_header_rebuild(). The headroom left after the push has to be at least skb->mac_len for that rebuild, but the three requests ask for the pushed length plus dst_dev_overhead(), which leaves LL_RESERVED_SPACE() of the egress device, 16 bytes for plain Ethernet. Where the mac header is longer than that, as it is on ingress through a VLAN device with reorder_hdr off, the rebuild runs out of room: skb_set_mac_header(skb, -skb->mac_len) computes a negative offset, stores it unchecked in the u16 skb->mac_header, and the memmove that follows writes skb->mac_len bytes about 64 KB past skb->head. Forwarding plain ping6 traffic through such a device reproduces it on all five encapsulation modes; skb->mac_header comes back as 65534 on a 704-byte head. Ask for whichever of the two is larger. These requests carried skb->mac_len until the egress overhead took its place rather than joining it. Fixes: 40475b63761a ("net: ipv6: seg6_iptunnel: mitigate 2-realloc issue") Assisted-by: LLM Signed-off-by: Yuya Kusakabe --- net/ipv6/seg6_iptunnel.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c index 61c6a27bf202..0e60bbca19ca 100644 --- a/net/ipv6/seg6_iptunnel.c +++ b/net/ipv6/seg6_iptunnel.c @@ -153,7 +153,8 @@ static int __seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, hdrlen = (osrh->hdrlen + 1) << 3; tot_len = hdrlen + sizeof(*hdr); - err = skb_cow_head(skb, tot_len + dst_dev_overhead(cache_dst, skb)); + err = skb_cow_head(skb, tot_len + max(skb->mac_len, + dst_dev_overhead(cache_dst, skb))); if (unlikely(err)) return err; @@ -255,7 +256,8 @@ static int seg6_do_srh_encap_red(struct sk_buff *skb, tot_len = red_hdrlen + sizeof(struct ipv6hdr); - err = skb_cow_head(skb, tot_len + dst_dev_overhead(cache_dst, skb)); + err = skb_cow_head(skb, tot_len + max(skb->mac_len, + dst_dev_overhead(cache_dst, skb))); if (unlikely(err)) return err; @@ -351,7 +353,8 @@ static int __seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, hdrlen = (osrh->hdrlen + 1) << 3; - err = skb_cow_head(skb, hdrlen + dst_dev_overhead(cache_dst, skb)); + err = skb_cow_head(skb, hdrlen + max(skb->mac_len, + dst_dev_overhead(cache_dst, skb))); if (unlikely(err)) return err; --- base-commit: 9a1599eeb8d18a2113e4cabcbd3bec5a8377dbed change-id: 20260917-seg6-maclen-headroom-53a339c17dac Best regards, -- Yuya Kusakabe