aya: tc: add qdisc_detach_program

qdisc_detach_program can be used to detach all the programs that have
the given name. It's useful when you want to detach programs that were
attached by some other process (eg. iproute2), or when you want to
detach programs that were previously left attached because the program
that attached them was killed.

aya/src/programs/tc.rs

@@ -8,7 +8,10 @@ use crate::{
         bpf_prog_type::BPF_PROG_TYPE_SCHED_CLS, TC_H_CLSACT, TC_H_MIN_EGRESS, TC_H_MIN_INGRESS,
     },
     programs::{load_program, Link, LinkRef, ProgramData, ProgramError},
-    sys::{netlink_qdisc_add_clsact, netlink_qdisc_attach, netlink_qdisc_detach},
+    sys::{
+        netlink_find_filter_with_name, netlink_qdisc_add_clsact, netlink_qdisc_attach,
+        netlink_qdisc_detach,
+    },
     util::{ifindex_from_ifname, tc_handler_make},
 };
 
@@ -130,6 +133,7 @@ impl SchedClassifier {
         let priority =
             unsafe { netlink_qdisc_attach(if_index as i32, &attach_type, prog_fd, &name) }
                 .map_err(|io_error| TcError::NetlinkError { io_error })?;
+
         Ok(self.data.link(TcLink {
             if_index: if_index as i32,
             attach_type,
@@ -165,3 +169,30 @@ pub fn qdisc_add_clsact(if_name: &str) -> Result<(), io::Error> {
     let if_index = ifindex_from_ifname(if_name)?;
     unsafe { netlink_qdisc_add_clsact(if_index as i32) }
 }
+
+/// Detaches the programs with the given name.
+///
+/// # Errors
+///
+/// Returns [`io::ErrorKind::NotFound`] to indicate that no programs with the
+/// given name were found, so nothing was detached. Other error kinds indicate
+/// an actual failure while detaching a program.
+pub fn qdisc_detach_program(
+    if_name: &str,
+    attach_type: TcAttachType,
+    name: &str,
+) -> Result<(), io::Error> {
+    let if_index = ifindex_from_ifname(if_name)? as i32;
+    let c_name = CString::new(name).unwrap();
+
+    let prios = unsafe { netlink_find_filter_with_name(if_index, attach_type, &c_name)? };
+    if prios.is_empty() {
+        return Err(io::Error::new(io::ErrorKind::NotFound, format!("{}", name)));
+    }
+
+    for prio in prios {
+        unsafe { netlink_qdisc_detach(if_index, &attach_type, prio)? };
+    }
+
+    Ok(())
+}

aya/src/sys/netlink.rs

@@ -1,11 +1,12 @@
-use std::{ffi::CStr, io, mem, os::unix::io::RawFd, ptr, slice};
+use std::{collections::HashMap, ffi::CStr, io, mem, os::unix::io::RawFd, ptr, slice};
+use thiserror::Error;
 
 use libc::{
     c_int, close, getsockname, nlattr, nlmsgerr, nlmsghdr, recv, send, setsockopt, sockaddr_nl,
     socket, AF_NETLINK, AF_UNSPEC, ETH_P_ALL, IFLA_XDP, NETLINK_ROUTE, NLA_ALIGNTO, NLA_F_NESTED,
-    NLMSG_DONE, NLMSG_ERROR, NLM_F_ACK, NLM_F_CREATE, NLM_F_ECHO, NLM_F_EXCL, NLM_F_MULTI,
-    NLM_F_REQUEST, RTM_DELTFILTER, RTM_NEWQDISC, RTM_NEWTFILTER, RTM_SETLINK, SOCK_RAW,
-    SOL_NETLINK,
+    NLA_TYPE_MASK, NLMSG_DONE, NLMSG_ERROR, NLM_F_ACK, NLM_F_CREATE, NLM_F_DUMP, NLM_F_ECHO,
+    NLM_F_EXCL, NLM_F_MULTI, NLM_F_REQUEST, RTM_DELTFILTER, RTM_GETTFILTER, RTM_NEWQDISC,
+    RTM_NEWTFILTER, RTM_SETLINK, SOCK_RAW, SOL_NETLINK,
 };
 
 use crate::{
@@ -192,6 +193,54 @@ pub(crate) unsafe fn netlink_qdisc_detach(
     Ok(())
 }
 
+pub(crate) unsafe fn netlink_find_filter_with_name(
+    if_index: i32,
+    attach_type: TcAttachType,
+    name: &CStr,
+) -> Result<Vec<u32>, io::Error> {
+    let mut req = mem::zeroed::<TcRequest>();
+
+    let nlmsg_len = mem::size_of::<nlmsghdr>() + mem::size_of::<tcmsg>();
+    req.header = nlmsghdr {
+        nlmsg_len: nlmsg_len as u32,
+        nlmsg_type: RTM_GETTFILTER,
+        nlmsg_flags: (NLM_F_REQUEST | NLM_F_DUMP) as u16,
+        nlmsg_pid: 0,
+        nlmsg_seq: 1,
+    };
+    req.tc_info.tcm_family = AF_UNSPEC as u8;
+    req.tc_info.tcm_handle = 0; // auto-assigned, if not provided
+    req.tc_info.tcm_ifindex = if_index;
+    req.tc_info.tcm_parent = attach_type.parent();
+
+    let sock = NetlinkSocket::open()?;
+    sock.send(&bytes_of(&req)[..req.header.nlmsg_len as usize])?;
+
+    let mut prios = Vec::new();
+    for msg in sock.recv()? {
+        if msg.header.nlmsg_type != RTM_NEWTFILTER {
+            continue;
+        }
+
+        let tc_msg = ptr::read_unaligned(msg.data.as_ptr() as *const tcmsg);
+        let priority = tc_msg.tcm_info >> 16;
+        let attrs = parse_attrs(&msg.data[mem::size_of::<tcmsg>()..])?;
+
+        if let Some(opts) = attrs.get(&(TCA_OPTIONS as u16)) {
+            let opts = parse_attrs(&opts.data)?;
+            if let Some(f_name) = opts.get(&(TCA_BPF_NAME as u16)) {
+                if let Ok(f_name) = CStr::from_bytes_with_nul(f_name.data) {
+                    if name == f_name {
+                        prios.push(priority);
+                    }
+                }
+            }
+        }
+    }
+
+    Ok(prios)
+}
+
 #[repr(C)]
 struct Request {
     header: nlmsghdr,
@@ -447,8 +496,84 @@ fn write_bytes(buf: &mut [u8], offset: usize, value: &[u8]) -> Result<usize, io:
 
     Ok(align_len)
 }
+
+struct NlAttrsIterator<'a> {
+    attrs: &'a [u8],
+    offset: usize,
+}
+
+impl<'a> NlAttrsIterator<'a> {
+    fn new(attrs: &[u8]) -> NlAttrsIterator {
+        NlAttrsIterator { attrs, offset: 0 }
+    }
+}
+
+impl<'a> Iterator for NlAttrsIterator<'a> {
+    type Item = Result<NlAttr<'a>, NlAttrError>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let buf = &self.attrs[self.offset..];
+        if buf.len() == 0 {
+            return None;
+        }
+
+        if NLA_HDR_LEN > buf.len() {
+            self.offset = buf.len();
+            return Some(Err(NlAttrError::InvalidBufferLength {
+                size: buf.len(),
+                expected: NLA_HDR_LEN,
+            }));
+        }
+
+        let attr = unsafe { ptr::read_unaligned(buf.as_ptr() as *const nlattr) };
+        let len = attr.nla_len as usize;
+        let align_len = align_to(len, NLA_ALIGNTO as usize);
+        if len < NLA_HDR_LEN {
+            return Some(Err(NlAttrError::InvalidHeaderLength(len)));
+        }
+        if align_len > buf.len() {
+            return Some(Err(NlAttrError::InvalidBufferLength {
+                size: buf.len(),
+                expected: align_len,
+            }));
+        }
+
+        let data = &buf[NLA_HDR_LEN..len];
+
+        self.offset += align_len;
+        Some(Ok(NlAttr { header: attr, data }))
+    }
+}
+
+fn parse_attrs(buf: &[u8]) -> Result<HashMap<u16, NlAttr>, NlAttrError> {
+    let mut attrs = HashMap::new();
+    for attr in NlAttrsIterator::new(buf) {
+        let attr = attr?;
+        attrs.insert(attr.header.nla_type & NLA_TYPE_MASK as u16, attr);
+    }
+    Ok(attrs)
+}
+
+#[derive(Clone)]
+struct NlAttr<'a> {
+    header: nlattr,
+    data: &'a [u8],
 }
 
+#[derive(Debug, Error, PartialEq)]
+enum NlAttrError {
+    #[error("invalid buffer size `{size}`, expected `{expected}`")]
+    InvalidBufferLength { size: usize, expected: usize },
+
+    #[error("invalid nlattr header length `{0}`")]
+    InvalidHeaderLength(usize),
+}
+
+impl From<NlAttrError> for io::Error {
+    fn from(e: NlAttrError) -> io::Error {
+        io::Error::new(io::ErrorKind::Other, e)
+    }
+}
 
 unsafe fn request_attributes<T>(req: &mut T, msg_len: usize) -> &mut [u8] {
     let attrs_addr = align_to(
@@ -463,8 +588,11 @@ fn bytes_of<T>(val: &T) -> &[u8] {
     let size = mem::size_of::<T>();
     unsafe { slice::from_raw_parts(slice::from_ref(val).as_ptr().cast(), size) }
 }
+
 #[cfg(test)]
 mod tests {
+    use std::{convert::TryInto, ffi::CString};
+
     use super::*;
 
     #[test]
@@ -510,4 +638,88 @@ mod tests {
         };
         assert_eq!(fd, 24);
     }
+
+    #[test]
+    fn test_nlattr_iterator_empty() {
+        let mut iter = NlAttrsIterator::new(&[]);
+        assert!(iter.next().is_none());
+    }
+
+    #[test]
+    fn test_nlattr_iterator_one() {
+        let mut buf = [0; NLA_HDR_LEN + mem::size_of::<u32>()];
+
+        write_attr(&mut buf, 0, IFLA_XDP_FD as u16, 42u32).unwrap();
+
+        let mut iter = NlAttrsIterator::new(&buf);
+        let attr = iter.next().unwrap().unwrap();
+        assert_eq!(attr.header.nla_type, IFLA_XDP_FD as u16);
+        assert_eq!(attr.data.len(), mem::size_of::<u32>());
+        assert_eq!(u32::from_ne_bytes(attr.data.try_into().unwrap()), 42);
+
+        assert!(iter.next().is_none());
+    }
+
+    #[test]
+    fn test_nlattr_iterator_many() {
+        let mut buf = [0; (NLA_HDR_LEN + mem::size_of::<u32>()) * 2];
+
+        write_attr(&mut buf, 0, IFLA_XDP_FD as u16, 42u32).unwrap();
+        write_attr(
+            &mut buf,
+            NLA_HDR_LEN + mem::size_of::<u32>(),
+            IFLA_XDP_EXPECTED_FD as u16,
+            12u32,
+        )
+        .unwrap();
+
+        let mut iter = NlAttrsIterator::new(&buf);
+
+        let attr = iter.next().unwrap().unwrap();
+        assert_eq!(attr.header.nla_type, IFLA_XDP_FD as u16);
+        assert_eq!(attr.data.len(), mem::size_of::<u32>());
+        assert_eq!(u32::from_ne_bytes(attr.data.try_into().unwrap()), 42);
+
+        let attr = iter.next().unwrap().unwrap();
+        assert_eq!(attr.header.nla_type, IFLA_XDP_EXPECTED_FD as u16);
+        assert_eq!(attr.data.len(), mem::size_of::<u32>());
+        assert_eq!(u32::from_ne_bytes(attr.data.try_into().unwrap()), 12);
+
+        assert!(iter.next().is_none());
+    }
+
+    #[test]
+    fn test_nlattr_iterator_nested() {
+        let mut buf = [0; 1024];
+
+        let mut options = NestedAttrs::new(&mut buf, TCA_OPTIONS as u16);
+        options.write_attr(TCA_BPF_FD as u16, 42).unwrap();
+
+        let name = CString::new("foo").unwrap();
+        options
+            .write_attr_bytes(TCA_BPF_NAME as u16, name.to_bytes_with_nul())
+            .unwrap();
+        options.finish().unwrap();
+
+        let mut iter = NlAttrsIterator::new(&buf);
+        let outer = iter.next().unwrap().unwrap();
+        assert_eq!(
+            outer.header.nla_type & NLA_TYPE_MASK as u16,
+            TCA_OPTIONS as u16
+        );
+
+        let mut iter = NlAttrsIterator::new(&outer.data);
+        let inner = iter.next().unwrap().unwrap();
+        assert_eq!(
+            inner.header.nla_type & NLA_TYPE_MASK as u16,
+            TCA_BPF_FD as u16
+        );
+        let inner = iter.next().unwrap().unwrap();
+        assert_eq!(
+            inner.header.nla_type & NLA_TYPE_MASK as u16,
+            TCA_BPF_NAME as u16
+        );
+        let name = CStr::from_bytes_with_nul(inner.data).unwrap();
+        assert_eq!(name.to_string_lossy(), "foo");
+    }
 }