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[59.124.8.50]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b9caaaec82sm96828415ad.24.2026.05.04.00.34.56 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 04 May 2026 00:35:00 -0700 (PDT) From: HexRabbit To: netdev@vger.kernel.org Cc: Steffen Klassert , Greg Kroah-Hartman , Herbert Xu , Simon Horman , "David S . Miller" , David Ahern , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Ido Schimmel , linux-kernel@vger.kernel.org, Kuan-Ting Chen Subject: [PATCH net] xfrm: esp: avoid in-place decrypt on shared skb frags Date: Mon, 4 May 2026 15:34:03 +0800 Message-ID: <20260504073403.38854-1-h3xrabbit@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Kuan-Ting Chen MSG_SPLICE_PAGES can attach pages from a pipe directly to an skb. TCP marks such skbs with SKBFL_SHARED_FRAG after skb_splice_from_iter(), so later paths that may modify packet data can first make a private copy. The IPv4/IPv6 datagram append paths did not set this flag when splicing pages into UDP skbs. That leaves an ESP-in-UDP packet made from shared pipe pages looking like an ordinary uncloned nonlinear skb. ESP input then takes the no-COW fast path for uncloned skbs without a frag_list and decrypts in place over data that is not owned privately by the skb. Mark IPv4/IPv6 datagram splice frags with SKBFL_SHARED_FRAG, matching TCP. Also make ESP input fall back to skb_cow_data() when the flag is present, so ESP does not decrypt externally backed frags in place. Private nonlinear skb frags still use the existing fast path. This intentionally does not change ESP output. In esp_output_head(), the path that appends the ESP trailer to existing skb tailroom without calling skb_cow_data() is not reachable for nonlinear skbs: skb_tailroom() returns zero when skb->data_len is nonzero, while ESP tailen is positive. Thus ESP output will either use the separate destination-frag path or fall back to skb_cow_data(). Signed-off-by: Kuan-Ting Chen Reported-by: Hyunwoo Kim --- net/ipv4/esp4.c | 3 ++- net/ipv4/ip_output.c | 2 ++ net/ipv6/esp6.c | 3 ++- net/ipv6/ip6_output.c | 2 ++ 4 files changed, 8 insertions(+), 2 deletions(-) diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c index 6dfc0bcde..6a5febbdb 100644 --- a/net/ipv4/esp4.c +++ b/net/ipv4/esp4.c @@ -873,7 +873,8 @@ static int esp_input(struct xfrm_state *x, struct sk_bu= ff *skb) nfrags =3D 1; =20 goto skip_cow; - } else if (!skb_has_frag_list(skb)) { + } else if (!skb_has_frag_list(skb) && + !skb_has_shared_frag(skb)) { nfrags =3D skb_shinfo(skb)->nr_frags; nfrags++; =20 diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c index e4790cc7b..5bcd73cbd 100644 --- a/net/ipv4/ip_output.c +++ b/net/ipv4/ip_output.c @@ -1233,6 +1233,8 @@ static int __ip_append_data(struct sock *sk, if (err < 0) goto error; copy =3D err; + if (!(flags & MSG_NO_SHARED_FRAGS)) + skb_shinfo(skb)->flags |=3D SKBFL_SHARED_FRAG; wmem_alloc_delta +=3D copy; } else if (!zc) { int i =3D skb_shinfo(skb)->nr_frags; diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c index 9f7531373..9c06c5a14 100644 --- a/net/ipv6/esp6.c +++ b/net/ipv6/esp6.c @@ -915,7 +915,8 @@ static int esp6_input(struct xfrm_state *x, struct sk_b= uff *skb) nfrags =3D 1; =20 goto skip_cow; - } else if (!skb_has_frag_list(skb)) { + } else if (!skb_has_frag_list(skb) && + !skb_has_shared_frag(skb)) { nfrags =3D skb_shinfo(skb)->nr_frags; nfrags++; =20 diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index 7e92909ab..1f2a33fbe 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -1794,6 +1794,8 @@ static int __ip6_append_data(struct sock *sk, if (err < 0) goto error; copy =3D err; + if (!(flags & MSG_NO_SHARED_FRAGS)) + skb_shinfo(skb)->flags |=3D SKBFL_SHARED_FRAG; wmem_alloc_delta +=3D copy; } else if (!zc) { int i =3D skb_shinfo(skb)->nr_frags; --=20 2.43.0