From a75d99f46bf21b45965ce39c5cfb3b8bb5ffb1aa Mon Sep 17 00:00:00 2001 From: Nuoqi Gui Date: Tue, 23 Jun 2026 18:32:31 +0800 Subject: [PATCH] seg6: validate SRH length before reading fixed fields seg6_validate_srh() reads fixed SRH fields such as srh->type and srh->hdrlen before checking that the supplied length covers the fixed struct ipv6_sr_hdr fields. The BPF SEG6 encap path reaches this with a BPF program-supplied pointer and length: bpf_lwt_push_encap() and the SEG6 local BPF END_B6 and END_B6_ENCAP actions call bpf_push_seg6_encap(), which forwards the length to seg6_validate_srh() with no minimum-size guard. A 2-byte SEG6 encap header can therefore make the validator read srh->type at offset 2 beyond the caller-supplied buffer. Reject lengths shorter than the fixed SRH at the top of seg6_validate_srh(), before any field is read. This fixes the BPF helper path and keeps the common validator robust. Fixes: fe94cc290f53 ("bpf: Add IPv6 Segment Routing helpers") Signed-off-by: Nuoqi Gui Reviewed-by: Andrea Mayer Link: https://patch.msgid.link/20260623-f01-17-seg6-srh-len-v2-1-2edc40e9e3e1@mails.tsinghua.edu.cn Signed-off-by: Jakub Kicinski --- net/ipv6/seg6.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/ipv6/seg6.c b/net/ipv6/seg6.c index 1c3ad25700c4..62a7eb779202 100644 --- a/net/ipv6/seg6.c +++ b/net/ipv6/seg6.c @@ -29,6 +29,9 @@ bool seg6_validate_srh(struct ipv6_sr_hdr *srh, int len, bool reduced) int max_last_entry; int trailing; + if (len < sizeof(*srh)) + return false; + if (srh->type != IPV6_SRCRT_TYPE_4) return false;