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Sun, 19 Apr 2026 08:03:50 -0700 (PDT) Received: from teatimelab.tailcd024.ts.net ([148.135.103.3]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2e53a4a8018sm12350791eec.8.2026.04.19.08.03.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 19 Apr 2026 08:03:49 -0700 (PDT) From: Qi Tang To: davem@davemloft.net, dsahern@kernel.org, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Qi Tang Subject: [PATCH net] ipv6: validate extension header length before copying to cmsg Date: Sun, 19 Apr 2026 23:03:44 +0800 Message-ID: <20260419150344.624673-1-tpluszz77@gmail.com> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ip6_datagram_recv_specific_ctl() builds IPV6_{HOPOPTS,DSTOPTS,RTHDR} cmsgs (and their IPV6_2292* legacy counterparts) by trusting the on-wire hdrlen byte (ptr[1]) when computing the put_cmsg() length. The length was validated only at parse time (ipv6_parse_hopopts(), etc.). An nftables payload-write expression can rewrite hdrlen after parsing and before the skb reaches recvmsg; the write itself is in-bounds but put_cmsg() then reads up to ((hdrlen+1) << 3) = 2040 bytes from an 8-byte header. nftables is reachable from an unprivi- leged user namespace, so this is an unprivileged slab-out-of-bounds read: BUG: KASAN: slab-out-of-bounds in put_cmsg+0x3ac/0x540 put_cmsg+0x3ac/0x540 udpv6_recvmsg+0xca0/0x1250 sock_recvmsg+0xdf/0x190 ____sys_recvmsg+0x1b1/0x620 Clamp each cmsg length against skb_tail_pointer(skb) before calling put_cmsg(). Extension headers are kept in the linear skb area by pskb_may_pull() during input, so skb_tail_pointer() is the correct bound. The check is replicated at each call site (one HbH, four RFC2292 sites, and four switch cases in the DSTOPTS/RTHDR/AH walk) rather than hoisted out of the switch, to keep the fix minimal and backportable; a follow-up cleanup can factor it out. In the walk loop a failed check also aborts the walk, since subsequent offsets depend on the tampered length. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Qi Tang --- net/ipv6/datagram.c | 35 ++++++++++++++++++++++++++++++----- 1 file changed, 30 insertions(+), 5 deletions(-) diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c index ca3605acb..a7b9f5a24 100644 --- a/net/ipv6/datagram.c +++ b/net/ipv6/datagram.c @@ -643,7 +643,10 @@ void ip6_datagram_recv_specific_ctl(struct sock *sk, struct msghdr *msg, /* HbH is allowed only once */ if (np->rxopt.bits.hopopts && (opt->flags & IP6SKB_HOPBYHOP)) { u8 *ptr = nh + sizeof(struct ipv6hdr); - put_cmsg(msg, SOL_IPV6, IPV6_HOPOPTS, (ptr[1]+1)<<3, ptr); + u16 hbhlen = (ptr[1] + 1) << 3; + + if (ptr + hbhlen <= skb_tail_pointer(skb)) + put_cmsg(msg, SOL_IPV6, IPV6_HOPOPTS, hbhlen, ptr); } if (opt->lastopt && @@ -668,27 +671,37 @@ void ip6_datagram_recv_specific_ctl(struct sock *sk, struct msghdr *msg, case IPPROTO_DSTOPTS: nexthdr = ptr[0]; len = (ptr[1] + 1) << 3; + if (ptr + len > skb_tail_pointer(skb)) + goto ext_hdr_done; if (np->rxopt.bits.dstopts) put_cmsg(msg, SOL_IPV6, IPV6_DSTOPTS, len, ptr); break; case IPPROTO_ROUTING: nexthdr = ptr[0]; len = (ptr[1] + 1) << 3; + if (ptr + len > skb_tail_pointer(skb)) + goto ext_hdr_done; if (np->rxopt.bits.srcrt) put_cmsg(msg, SOL_IPV6, IPV6_RTHDR, len, ptr); break; case IPPROTO_AH: nexthdr = ptr[0]; len = (ptr[1] + 2) << 2; + if (ptr + len > skb_tail_pointer(skb)) + goto ext_hdr_done; break; default: nexthdr = ptr[0]; len = (ptr[1] + 1) << 3; + if (ptr + len > skb_tail_pointer(skb)) + goto ext_hdr_done; break; } off += len; } +ext_hdr_done: + ; } /* socket options in old style */ @@ -705,19 +718,31 @@ void ip6_datagram_recv_specific_ctl(struct sock *sk, struct msghdr *msg, } if (np->rxopt.bits.ohopopts && (opt->flags & IP6SKB_HOPBYHOP)) { u8 *ptr = nh + sizeof(struct ipv6hdr); - put_cmsg(msg, SOL_IPV6, IPV6_2292HOPOPTS, (ptr[1]+1)<<3, ptr); + u16 hbhlen = (ptr[1] + 1) << 3; + + if (ptr + hbhlen <= skb_tail_pointer(skb)) + put_cmsg(msg, SOL_IPV6, IPV6_2292HOPOPTS, hbhlen, ptr); } if (np->rxopt.bits.odstopts && opt->dst0) { u8 *ptr = nh + opt->dst0; - put_cmsg(msg, SOL_IPV6, IPV6_2292DSTOPTS, (ptr[1]+1)<<3, ptr); + u16 doptlen = (ptr[1] + 1) << 3; + + if (ptr + doptlen <= skb_tail_pointer(skb)) + put_cmsg(msg, SOL_IPV6, IPV6_2292DSTOPTS, doptlen, ptr); } if (np->rxopt.bits.osrcrt && opt->srcrt) { struct ipv6_rt_hdr *rthdr = (struct ipv6_rt_hdr *)(nh + opt->srcrt); - put_cmsg(msg, SOL_IPV6, IPV6_2292RTHDR, (rthdr->hdrlen+1) << 3, rthdr); + u16 rtlen = (rthdr->hdrlen + 1) << 3; + + if ((u8 *)rthdr + rtlen <= skb_tail_pointer(skb)) + put_cmsg(msg, SOL_IPV6, IPV6_2292RTHDR, rtlen, rthdr); } if (np->rxopt.bits.odstopts && opt->dst1) { u8 *ptr = nh + opt->dst1; - put_cmsg(msg, SOL_IPV6, IPV6_2292DSTOPTS, (ptr[1]+1)<<3, ptr); + u16 doptlen = (ptr[1] + 1) << 3; + + if (ptr + doptlen <= skb_tail_pointer(skb)) + put_cmsg(msg, SOL_IPV6, IPV6_2292DSTOPTS, doptlen, ptr); } if (np->rxopt.bits.rxorigdstaddr) { struct sockaddr_in6 sin6; -- 2.47.3