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[34.85.134.180]) by smtp.gmail.com with UTF8SMTPSA id 00721157ae682-79a715d6acfsm37639657b3.40.2026.03.19.06.24.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Mar 2026 06:24:39 -0700 (PDT) Date: Thu, 19 Mar 2026 09:24:39 -0400 From: Willem de Bruijn To: "Hudson, Nick" , Willem de Bruijn Cc: "bpf@vger.kernel.org" , "netdev@vger.kernel.org" , "Tottenham, Max" , "Glasgall, Anna" , Martin KaFai Lau , Daniel Borkmann , Alexei Starovoitov , Andrii Nakryiko , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , "linux-kernel@vger.kernel.org" Message-ID: In-Reply-To: <03A3369E-0F7B-4708-92B9-B335A6F86976@akamai.com> References: <20260318134242.2725749-1-nhudson@akamai.com> <20260318134242.2725749-5-nhudson@akamai.com> <03A3369E-0F7B-4708-92B9-B335A6F86976@akamai.com> Subject: Re: [PATCH v2 4/5] bpf: allow new DECAP flags and add guard rails Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Hudson, Nick wrote: > > > > On 18 Mar 2026, at 20:02, Willem de Bruijn wrote: > > > > !-------------------------------------------------------------------| > > This Message Is From an External Sender > > This message came from outside your organization. > > |-------------------------------------------------------------------! > > > > Nick Hudson wrote: > >> Add checks to require shrink-only decap, reject conflicting decap flag > >> combinations, and verify removed length is sufficient for claimed header > >> decapsulation. > >> > >> Co-developed-by: Max Tottenham > >> Signed-off-by: Max Tottenham > >> Co-developed-by: Anna Glasgall > >> Signed-off-by: Anna Glasgall > >> Signed-off-by: Nick Hudson > >> --- > >> net/core/filter.c | 47 +++++++++++++++++++++++++++++++++++++---------- > >> 1 file changed, 37 insertions(+), 10 deletions(-) > >> > >> diff --git a/net/core/filter.c b/net/core/filter.c > >> index 7c2871b40fe4..47aec44a9cd3 100644 > >> --- a/net/core/filter.c > >> +++ b/net/core/filter.c > >> @@ -56,6 +56,7 @@ > >> #include > >> #include > >> #include > >> +#include > >> #include > >> #include > >> #include > >> @@ -3496,7 +3497,9 @@ static u32 bpf_skb_net_base_len(const struct sk_buff *skb) > >> BPF_F_ADJ_ROOM_ENCAP_L2( \ > >> BPF_ADJ_ROOM_ENCAP_L2_MASK)) > >> > >> -#define BPF_F_ADJ_ROOM_DECAP_MASK (BPF_F_ADJ_ROOM_DECAP_L3_MASK) > >> +#define BPF_F_ADJ_ROOM_DECAP_MASK (BPF_F_ADJ_ROOM_DECAP_L3_MASK | \ > >> + BPF_F_ADJ_ROOM_DECAP_L4_MASK | \ > >> + BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK) > >> > >> #define BPF_F_ADJ_ROOM_MASK (BPF_F_ADJ_ROOM_FIXED_GSO | \ > >> BPF_F_ADJ_ROOM_ENCAP_MASK | \ > >> @@ -3743,20 +3746,44 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, > >> return -ENOTSUPP; > >> } > >> > >> - if (flags & BPF_F_ADJ_ROOM_DECAP_L3_MASK) { > >> + if (flags & BPF_F_ADJ_ROOM_DECAP_MASK) { > >> + u32 len_decap_min = 0; > >> + > >> if (!shrink) > >> return -EINVAL; > >> > >> - switch (flags & BPF_F_ADJ_ROOM_DECAP_L3_MASK) { > >> - case BPF_F_ADJ_ROOM_DECAP_L3_IPV4: > >> + /* Reject mutually exclusive decap flag pairs. */ > >> + if ((flags & BPF_F_ADJ_ROOM_DECAP_L3_MASK) == > >> + BPF_F_ADJ_ROOM_DECAP_L3_MASK) > >> + return -EINVAL; > >> + > >> + if ((flags & BPF_F_ADJ_ROOM_DECAP_L4_MASK) == > >> + BPF_F_ADJ_ROOM_DECAP_L4_MASK) > >> + return -EINVAL; > >> + > >> + if ((flags & BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK) == > >> + BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK) > >> + return -EINVAL; > >> + > >> + /* Reject mutually exclusive decap tunnel type flags. */ > >> + if ((flags & BPF_F_ADJ_ROOM_DECAP_L4_MASK) && > >> + (flags & BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK)) > >> + return -EINVAL; > >> + > >> + if (flags & BPF_F_ADJ_ROOM_DECAP_L4_UDP) > >> + len_decap_min += sizeof(struct udphdr); > >> + > >> + if (flags & BPF_F_ADJ_ROOM_DECAP_L4_GRE) > >> + len_decap_min += sizeof(struct gre_base_hdr); > >> + > >> + if (len_diff_abs < len_decap_min) > >> + return -EINVAL; > > > > Should this test come after the below IP flags? > > Should it? > > Seems to me it can bail early without having to check the IP flags. len_decap_min vs len_min. > > What am I missing? I would think it common that UDP decap also includes an L3 decap, in which case the len_decap_min should include both header lengths.