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[2a01:110f:4809:d800::e00]) by smtp.gmail.com with ESMTPSA id f11sm2339618lfg.132.2022.01.30.03.55.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 30 Jan 2022 03:55:20 -0800 (PST) From: Jakub Sitnicki To: bpf@vger.kernel.org Cc: netdev@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Menglong Dong , Martin KaFai Lau Subject: [PATCH bpf-next v2 1/2] bpf: Make dst_port field in struct bpf_sock 16-bit wide Date: Sun, 30 Jan 2022 12:55:17 +0100 Message-Id: <20220130115518.213259-2-jakub@cloudflare.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20220130115518.213259-1-jakub@cloudflare.com> References: <20220130115518.213259-1-jakub@cloudflare.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net Menglong Dong reports that the documentation for the dst_port field in struct bpf_sock is inaccurate and confusing. From the BPF program PoV, the field is a zero-padded 16-bit integer in network byte order. The value appears to the BPF user as if laid out in memory as so: offsetof(struct bpf_sock, dst_port) + 0 + 8 +16 0x00 +24 0x00 32-, 16-, and 8-bit wide loads from the field are all allowed, but only if the offset into the field is 0. 32-bit wide loads from dst_port are especially confusing. The loaded value, after converting to host byte order with bpf_ntohl(dst_port), contains the port number in the upper 16-bits. Remove the confusion by splitting the field into two 16-bit fields. For backward compatibility, allow 32-bit wide loads from offsetof(struct bpf_sock, dst_port). While at it, allow loads 8-bit loads at offset [0] and [1] from dst_port. Reported-by: Menglong Dong Signed-off-by: Jakub Sitnicki --- include/uapi/linux/bpf.h | 3 ++- net/core/filter.c | 10 +++++++++- 2 files changed, 11 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 4a2f7041ebae..a7f0ddedac1f 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -5574,7 +5574,8 @@ struct bpf_sock { __u32 src_ip4; __u32 src_ip6[4]; __u32 src_port; /* host byte order */ - __u32 dst_port; /* network byte order */ + __be16 dst_port; /* network byte order */ + __u16 :16; /* zero padding */ __u32 dst_ip4; __u32 dst_ip6[4]; __u32 state; diff --git a/net/core/filter.c b/net/core/filter.c index a06931c27eeb..99a05199a806 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -8265,6 +8265,7 @@ bool bpf_sock_is_valid_access(int off, int size, enum bpf_access_type type, struct bpf_insn_access_aux *info) { const int size_default = sizeof(__u32); + int field_size; if (off < 0 || off >= sizeof(struct bpf_sock)) return false; @@ -8276,7 +8277,6 @@ bool bpf_sock_is_valid_access(int off, int size, enum bpf_access_type type, case offsetof(struct bpf_sock, family): case offsetof(struct bpf_sock, type): case offsetof(struct bpf_sock, protocol): - case offsetof(struct bpf_sock, dst_port): case offsetof(struct bpf_sock, src_port): case offsetof(struct bpf_sock, rx_queue_mapping): case bpf_ctx_range(struct bpf_sock, src_ip4): @@ -8285,6 +8285,14 @@ bool bpf_sock_is_valid_access(int off, int size, enum bpf_access_type type, case bpf_ctx_range_till(struct bpf_sock, dst_ip6[0], dst_ip6[3]): bpf_ctx_record_field_size(info, size_default); return bpf_ctx_narrow_access_ok(off, size, size_default); + case bpf_ctx_range(struct bpf_sock, dst_port): + field_size = size == size_default ? + size_default : sizeof_field(struct bpf_sock, dst_port); + bpf_ctx_record_field_size(info, field_size); + return bpf_ctx_narrow_access_ok(off, size, field_size); + case offsetofend(struct bpf_sock, dst_port) ... + offsetof(struct bpf_sock, dst_ip4) - 1: + return false; } return size == size_default;