aboutsummaryrefslogtreecommitdiff
path: root/Documentation/networking/dns_resolver.rst
diff options
context:
space:
mode:
authorLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
committerLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
commit5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 (patch)
treecc5c2d0a898769fd59549594fedb3ee6f84e59a0 /Documentation/networking/dns_resolver.rst
downloadlinux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.tar.gz
linux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.zip
Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-nextgrafted
Pull networking updates from Jakub Kicinski: "Core: - Add dedicated kmem_cache for typical/small skb->head, avoid having to access struct page at kfree time, and improve memory use. - Introduce sysctl to set default RPS configuration for new netdevs. - Define Netlink protocol specification format which can be used to describe messages used by each family and auto-generate parsers. Add tools for generating kernel data structures and uAPI headers. - Expose all net/core sysctls inside netns. - Remove 4s sleep in netpoll if carrier is instantly detected on boot. - Add configurable limit of MDB entries per port, and port-vlan. - Continue populating drop reasons throughout the stack. - Retire a handful of legacy Qdiscs and classifiers. Protocols: - Support IPv4 big TCP (TSO frames larger than 64kB). - Add IP_LOCAL_PORT_RANGE socket option, to control local port range on socket by socket basis. - Track and report in procfs number of MPTCP sockets used. - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path manager. - IPv6: don't check net.ipv6.route.max_size and rely on garbage collection to free memory (similarly to IPv4). - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986). - ICMP: add per-rate limit counters. - Add support for user scanning requests in ieee802154. - Remove static WEP support. - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate reporting. - WiFi 7 EHT channel puncturing support (client & AP). BPF: - Add a rbtree data structure following the "next-gen data structure" precedent set by recently added linked list, that is, by using kfunc + kptr instead of adding a new BPF map type. - Expose XDP hints via kfuncs with initial support for RX hash and timestamp metadata. - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to better support decap on GRE tunnel devices not operating in collect metadata. - Improve x86 JIT's codegen for PROBE_MEM runtime error checks. - Remove the need for trace_printk_lock for bpf_trace_printk and bpf_trace_vprintk helpers. - Extend libbpf's bpf_tracing.h support for tracing arguments of kprobes/uprobes and syscall as a special case. - Significantly reduce the search time for module symbols by livepatch and BPF. - Enable cpumasks to be used as kptrs, which is useful for tracing programs tracking which tasks end up running on which CPUs in different time intervals. - Add support for BPF trampoline on s390x and riscv64. - Add capability to export the XDP features supported by the NIC. - Add __bpf_kfunc tag for marking kernel functions as kfuncs. - Add cgroup.memory=nobpf kernel parameter option to disable BPF memory accounting for container environments. Netfilter: - Remove the CLUSTERIP target. It has been marked as obsolete for years, and we still have WARN splats wrt races of the out-of-band /proc interface installed by this target. - Add 'destroy' commands to nf_tables. They are identical to the existing 'delete' commands, but do not return an error if the referenced object (set, chain, rule...) did not exist. Driver API: - Improve cpumask_local_spread() locality to help NICs set the right IRQ affinity on AMD platforms. - Separate C22 and C45 MDIO bus transactions more clearly. - Introduce new DCB table to control DSCP rewrite on egress. - Support configuration of Physical Layer Collision Avoidance (PLCA) Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of shared medium Ethernet. - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing preemption of low priority frames by high priority frames. - Add support for controlling MACSec offload using netlink SET. - Rework devlink instance refcounts to allow registration and de-registration under the instance lock. Split the code into multiple files, drop some of the unnecessarily granular locks and factor out common parts of netlink operation handling. - Add TX frame aggregation parameters (for USB drivers). - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning messages with notifications for debug. - Allow offloading of UDP NEW connections via act_ct. - Add support for per action HW stats in TC. - Support hardware miss to TC action (continue processing in SW from a specific point in the action chain). - Warn if old Wireless Extension user space interface is used with modern cfg80211/mac80211 drivers. Do not support Wireless Extensions for Wi-Fi 7 devices at all. Everyone should switch to using nl80211 interface instead. - Improve the CAN bit timing configuration. Use extack to return error messages directly to user space, update the SJW handling, including the definition of a new default value that will benefit CAN-FD controllers, by increasing their oscillator tolerance. New hardware / drivers: - Ethernet: - nVidia BlueField-3 support (control traffic driver) - Ethernet support for imx93 SoCs - Motorcomm yt8531 gigabit Ethernet PHY - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA) - Microchip LAN8841 PHY (incl. cable diagnostics and PTP) - Amlogic gxl MDIO mux - WiFi: - RealTek RTL8188EU (rtl8xxxu) - Qualcomm Wi-Fi 7 devices (ath12k) - CAN: - Renesas R-Car V4H Drivers: - Bluetooth: - Set Per Platform Antenna Gain (PPAG) for Intel controllers. - Ethernet NICs: - Intel (1G, igc): - support TSN / Qbv / packet scheduling features of i226 model - Intel (100G, ice): - use GNSS subsystem instead of TTY - multi-buffer XDP support - extend support for GPIO pins to E823 devices - nVidia/Mellanox: - update the shared buffer configuration on PFC commands - implement PTP adjphase function for HW offset control - TC support for Geneve and GRE with VF tunnel offload - more efficient crypto key management method - multi-port eswitch support - Netronome/Corigine: - add DCB IEEE support - support IPsec offloading for NFP3800 - Freescale/NXP (enetc): - support XDP_REDIRECT for XDP non-linear buffers - improve reconfig, avoid link flap and waiting for idle - support MAC Merge layer - Other NICs: - sfc/ef100: add basic devlink support for ef100 - ionic: rx_push mode operation (writing descriptors via MMIO) - bnxt: use the auxiliary bus abstraction for RDMA - r8169: disable ASPM and reset bus in case of tx timeout - cpsw: support QSGMII mode for J721e CPSW9G - cpts: support pulse-per-second output - ngbe: add an mdio bus driver - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing - r8152: handle devices with FW with NCM support - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation - virtio-net: support multi buffer XDP - virtio/vsock: replace virtio_vsock_pkt with sk_buff - tsnep: XDP support - Ethernet high-speed switches: - nVidia/Mellanox (mlxsw): - add support for latency TLV (in FW control messages) - Microchip (sparx5): - separate explicit and implicit traffic forwarding rules, make the implicit rules always active - add support for egress DSCP rewrite - IS0 VCAP support (Ingress Classification) - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS etc.) - ES2 VCAP support (Egress Access Control) - support for Per-Stream Filtering and Policing (802.1Q, 8.6.5.1) - Ethernet embedded switches: - Marvell (mv88e6xxx): - add MAB (port auth) offload support - enable PTP receive for mv88e6390 - NXP (ocelot): - support MAC Merge layer - support for the the vsc7512 internal copper phys - Microchip: - lan9303: convert to PHYLINK - lan966x: support TC flower filter statistics - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x - lan937x: support Credit Based Shaper configuration - ksz9477: support Energy Efficient Ethernet - other: - qca8k: convert to regmap read/write API, use bulk operations - rswitch: Improve TX timestamp accuracy - Intel WiFi (iwlwifi): - EHT (Wi-Fi 7) rate reporting - STEP equalizer support: transfer some STEP (connection to radio on platforms with integrated wifi) related parameters from the BIOS to the firmware. - Qualcomm 802.11ax WiFi (ath11k): - IPQ5018 support - Fine Timing Measurement (FTM) responder role support - channel 177 support - MediaTek WiFi (mt76): - per-PHY LED support - mt7996: EHT (Wi-Fi 7) support - Wireless Ethernet Dispatch (WED) reset support - switch to using page pool allocator - RealTek WiFi (rtw89): - support new version of Bluetooth co-existance - Mobile: - rmnet: support TX aggregation" * tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits) page_pool: add a comment explaining the fragment counter usage net: ethtool: fix __ethtool_dev_mm_supported() implementation ethtool: pse-pd: Fix double word in comments xsk: add linux/vmalloc.h to xsk.c sefltests: netdevsim: wait for devlink instance after netns removal selftest: fib_tests: Always cleanup before exit net/mlx5e: Align IPsec ASO result memory to be as required by hardware net/mlx5e: TC, Set CT miss to the specific ct action instance net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG net/mlx5: Refactor tc miss handling to a single function net/mlx5: Kconfig: Make tc offload depend on tc skb extension net/sched: flower: Support hardware miss to tc action net/sched: flower: Move filter handle initialization earlier net/sched: cls_api: Support hardware miss to tc action net/sched: Rename user cookie and act cookie sfc: fix builds without CONFIG_RTC_LIB sfc: clean up some inconsistent indentings net/mlx4_en: Introduce flexible array to silence overflow warning net: lan966x: Fix possible deadlock inside PTP net/ulp: Remove redundant ->clone() test in inet_clone_ulp(). ...
Diffstat (limited to 'Documentation/networking/dns_resolver.rst')
-rw-r--r--Documentation/networking/dns_resolver.rst155
1 files changed, 155 insertions, 0 deletions
diff --git a/Documentation/networking/dns_resolver.rst b/Documentation/networking/dns_resolver.rst
new file mode 100644
index 000000000..add4d59a9
--- /dev/null
+++ b/Documentation/networking/dns_resolver.rst
@@ -0,0 +1,155 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================
+DNS Resolver Module
+===================
+
+.. Contents:
+
+ - Overview.
+ - Compilation.
+ - Setting up.
+ - Usage.
+ - Mechanism.
+ - Debugging.
+
+
+Overview
+========
+
+The DNS resolver module provides a way for kernel services to make DNS queries
+by way of requesting a key of key type dns_resolver. These queries are
+upcalled to userspace through /sbin/request-key.
+
+These routines must be supported by userspace tools dns.upcall, cifs.upcall and
+request-key. It is under development and does not yet provide the full feature
+set. The features it does support include:
+
+ (*) Implements the dns_resolver key_type to contact userspace.
+
+It does not yet support the following AFS features:
+
+ (*) Dns query support for AFSDB resource record.
+
+This code is extracted from the CIFS filesystem.
+
+
+Compilation
+===========
+
+The module should be enabled by turning on the kernel configuration options::
+
+ CONFIG_DNS_RESOLVER - tristate "DNS Resolver support"
+
+
+Setting up
+==========
+
+To set up this facility, the /etc/request-key.conf file must be altered so that
+/sbin/request-key can appropriately direct the upcalls. For example, to handle
+basic dname to IPv4/IPv6 address resolution, the following line should be
+added::
+
+
+ #OP TYPE DESC CO-INFO PROGRAM ARG1 ARG2 ARG3 ...
+ #====== ============ ======= ======= ==========================
+ create dns_resolver * * /usr/sbin/cifs.upcall %k
+
+To direct a query for query type 'foo', a line of the following should be added
+before the more general line given above as the first match is the one taken::
+
+ create dns_resolver foo:* * /usr/sbin/dns.foo %k
+
+
+Usage
+=====
+
+To make use of this facility, one of the following functions that are
+implemented in the module can be called after doing::
+
+ #include <linux/dns_resolver.h>
+
+ ::
+
+ int dns_query(const char *type, const char *name, size_t namelen,
+ const char *options, char **_result, time_t *_expiry);
+
+ This is the basic access function. It looks for a cached DNS query and if
+ it doesn't find it, it upcalls to userspace to make a new DNS query, which
+ may then be cached. The key description is constructed as a string of the
+ form::
+
+ [<type>:]<name>
+
+ where <type> optionally specifies the particular upcall program to invoke,
+ and thus the type of query to do, and <name> specifies the string to be
+ looked up. The default query type is a straight hostname to IP address
+ set lookup.
+
+ The name parameter is not required to be a NUL-terminated string, and its
+ length should be given by the namelen argument.
+
+ The options parameter may be NULL or it may be a set of options
+ appropriate to the query type.
+
+ The return value is a string appropriate to the query type. For instance,
+ for the default query type it is just a list of comma-separated IPv4 and
+ IPv6 addresses. The caller must free the result.
+
+ The length of the result string is returned on success, and a negative
+ error code is returned otherwise. -EKEYREJECTED will be returned if the
+ DNS lookup failed.
+
+ If _expiry is non-NULL, the expiry time (TTL) of the result will be
+ returned also.
+
+The kernel maintains an internal keyring in which it caches looked up keys.
+This can be cleared by any process that has the CAP_SYS_ADMIN capability by
+the use of KEYCTL_KEYRING_CLEAR on the keyring ID.
+
+
+Reading DNS Keys from Userspace
+===============================
+
+Keys of dns_resolver type can be read from userspace using keyctl_read() or
+"keyctl read/print/pipe".
+
+
+Mechanism
+=========
+
+The dnsresolver module registers a key type called "dns_resolver". Keys of
+this type are used to transport and cache DNS lookup results from userspace.
+
+When dns_query() is invoked, it calls request_key() to search the local
+keyrings for a cached DNS result. If that fails to find one, it upcalls to
+userspace to get a new result.
+
+Upcalls to userspace are made through the request_key() upcall vector, and are
+directed by means of configuration lines in /etc/request-key.conf that tell
+/sbin/request-key what program to run to instantiate the key.
+
+The upcall handler program is responsible for querying the DNS, processing the
+result into a form suitable for passing to the keyctl_instantiate_key()
+routine. This then passes the data to dns_resolver_instantiate() which strips
+off and processes any options included in the data, and then attaches the
+remainder of the string to the key as its payload.
+
+The upcall handler program should set the expiry time on the key to that of the
+lowest TTL of all the records it has extracted a result from. This means that
+the key will be discarded and recreated when the data it holds has expired.
+
+dns_query() returns a copy of the value attached to the key, or an error if
+that is indicated instead.
+
+See <file:Documentation/security/keys/request-key.rst> for further
+information about request-key function.
+
+
+Debugging
+=========
+
+Debugging messages can be turned on dynamically by writing a 1 into the
+following file::
+
+ /sys/module/dnsresolver/parameters/debug