recvmsg: Check if CMSG buffer was too small and return an error (#2413)

If MSG_CTRUNC is set, it is not safe to iterate the cmsgs, since they
could have been truncated. Change RecvMsg::cmsgs() to return a Result,
and to check for this flag (an API change).

Update tests for API change. Add test for too-small buffer.

Author: agrover

changelog/2413.changed.md

@@ -0,0 +1 @@
+`RecvMsg::cmsgs()` now returns a `Result`, and checks that cmsgs were not truncated.

src/sys/socket/mod.rs

@@ -13,6 +13,7 @@ use libc::{self, c_int, size_t, socklen_t};
 #[cfg(all(feature = "uio", not(target_os = "redox")))]
 use libc::{
     c_void, iovec, CMSG_DATA, CMSG_FIRSTHDR, CMSG_LEN, CMSG_NXTHDR, CMSG_SPACE,
+    MSG_CTRUNC,
 };
 #[cfg(not(target_os = "redox"))]
 use std::io::{IoSlice, IoSliceMut};
@@ -599,13 +600,19 @@ pub struct RecvMsg<'a, 's, S> {
 }
 
 impl<'a, S> RecvMsg<'a, '_, S> {
-    /// Iterate over the valid control messages pointed to by this
-    /// msghdr.
-    pub fn cmsgs(&self) -> CmsgIterator {
-        CmsgIterator {
+    /// Iterate over the valid control messages pointed to by this msghdr. If
+    /// allocated space for CMSGs was too small it is not safe to iterate,
+    /// instead return an `Error::ENOBUFS` error.
+    pub fn cmsgs(&self) -> Result<CmsgIterator> {
+
+        if self.mhdr.msg_flags & MSG_CTRUNC == MSG_CTRUNC {
+            return Err(Errno::ENOBUFS);
+        }
+
+        Ok(CmsgIterator {
             cmsghdr: self.cmsghdr,
             mhdr: &self.mhdr
-        }
+        })
     }
 }
 
@@ -700,7 +707,7 @@ pub enum ControlMessageOwned {
     /// let mut iov = [IoSliceMut::new(&mut buffer)];
     /// let r = recvmsg::<SockaddrIn>(in_socket.as_raw_fd(), &mut iov, Some(&mut cmsgspace), flags)
     ///     .unwrap();
-    /// let rtime = match r.cmsgs().next() {
+    /// let rtime = match r.cmsgs().unwrap().next() {
     ///     Some(ControlMessageOwned::ScmTimestamp(rtime)) => rtime,
     ///     Some(_) => panic!("Unexpected control message"),
     ///     None => panic!("No control message")

test/sys/test_socket.rs

@@ -55,7 +55,7 @@ pub fn test_timestamping() {
             .unwrap();
 
     let mut ts = None;
-    for c in recv.cmsgs() {
+    for c in recv.cmsgs().unwrap() {
         if let ControlMessageOwned::ScmTimestampsns(timestamps) = c {
             ts = Some(timestamps.system);
         }
@@ -117,7 +117,7 @@ pub fn test_timestamping_realtime() {
             .unwrap();
 
     let mut ts = None;
-    for c in recv.cmsgs() {
+    for c in recv.cmsgs().unwrap() {
         if let ControlMessageOwned::ScmRealtime(timeval) = c {
             ts = Some(timeval);
         }
@@ -179,7 +179,7 @@ pub fn test_timestamping_monotonic() {
             .unwrap();
 
     let mut ts = None;
-    for c in recv.cmsgs() {
+    for c in recv.cmsgs().unwrap() {
         if let ControlMessageOwned::ScmMonotonic(timeval) = c {
             ts = Some(timeval);
         }
@@ -889,7 +889,7 @@ pub fn test_scm_rights() {
         )
         .unwrap();
 
-        for cmsg in msg.cmsgs() {
+        for cmsg in msg.cmsgs().unwrap() {
             if let ControlMessageOwned::ScmRights(fd) = cmsg {
                 assert_eq!(received_r, None);
                 assert_eq!(fd.len(), 1);
@@ -1330,7 +1330,7 @@ fn test_scm_rights_single_cmsg_multiple_fds() {
             .flags
             .intersects(MsgFlags::MSG_TRUNC | MsgFlags::MSG_CTRUNC));
 
-        let mut cmsgs = msg.cmsgs();
+        let mut cmsgs = msg.cmsgs().unwrap();
         match cmsgs.next() {
             Some(ControlMessageOwned::ScmRights(fds)) => {
                 assert_eq!(
@@ -1399,7 +1399,7 @@ pub fn test_sendmsg_empty_cmsgs() {
         )
         .unwrap();
 
-        if msg.cmsgs().next().is_some() {
+        if msg.cmsgs().unwrap().next().is_some() {
             panic!("unexpected cmsg");
         }
         assert!(!msg
@@ -1466,7 +1466,7 @@ fn test_scm_credentials() {
         .unwrap();
         let mut received_cred = None;
 
-        for cmsg in msg.cmsgs() {
+        for cmsg in msg.cmsgs().unwrap() {
             let cred = match cmsg {
                 #[cfg(linux_android)]
                 ControlMessageOwned::ScmCredentials(cred) => cred,
@@ -1497,7 +1497,7 @@ fn test_scm_credentials() {
 #[test]
 fn test_scm_credentials_and_rights() {
     let space = cmsg_space!(libc::ucred, RawFd);
-    test_impl_scm_credentials_and_rights(space);
+    test_impl_scm_credentials_and_rights(space).unwrap();
 }
 
 /// Ensure that passing a an oversized control message buffer to recvmsg
@@ -1509,11 +1509,23 @@ fn test_scm_credentials_and_rights() {
 #[test]
 fn test_too_large_cmsgspace() {
     let space = vec![0u8; 1024];
-    test_impl_scm_credentials_and_rights(space);
+    test_impl_scm_credentials_and_rights(space).unwrap();
 }
 
 #[cfg(linux_android)]
-fn test_impl_scm_credentials_and_rights(mut space: Vec<u8>) {
+#[test]
+fn test_too_small_cmsgspace() {
+    let space = vec![0u8; 4];
+    assert_eq!(
+        test_impl_scm_credentials_and_rights(space),
+        Err(nix::errno::Errno::ENOBUFS)
+    );
+}
+
+#[cfg(linux_android)]
+fn test_impl_scm_credentials_and_rights(
+    mut space: Vec<u8>,
+) -> Result<(), nix::errno::Errno> {
     use libc::ucred;
     use nix::sys::socket::sockopt::PassCred;
     use nix::sys::socket::{
@@ -1573,9 +1585,9 @@ fn test_impl_scm_credentials_and_rights(mut space: Vec<u8>) {
         .unwrap();
         let mut received_cred = None;
 
-        assert_eq!(msg.cmsgs().count(), 2, "expected 2 cmsgs");
+        assert_eq!(msg.cmsgs()?.count(), 2, "expected 2 cmsgs");
 
-        for cmsg in msg.cmsgs() {
+        for cmsg in msg.cmsgs()? {
             match cmsg {
                 ControlMessageOwned::ScmRights(fds) => {
                     assert_eq!(received_r, None, "already received fd");
@@ -1606,6 +1618,8 @@ fn test_impl_scm_credentials_and_rights(mut space: Vec<u8>) {
     read(received_r.as_raw_fd(), &mut buf).unwrap();
     assert_eq!(&buf[..], b"world");
     close(received_r).unwrap();
+
+    Ok(())
 }
 
 // Test creating and using named unix domain sockets
@@ -1837,7 +1851,7 @@ pub fn test_recv_ipv4pktinfo() {
             .flags
             .intersects(MsgFlags::MSG_TRUNC | MsgFlags::MSG_CTRUNC));
 
-        let mut cmsgs = msg.cmsgs();
+        let mut cmsgs = msg.cmsgs().unwrap();
         if let Some(ControlMessageOwned::Ipv4PacketInfo(pktinfo)) = cmsgs.next()
         {
             let i = if_nametoindex(lo_name.as_bytes()).expect("if_nametoindex");
@@ -1929,11 +1943,11 @@ pub fn test_recvif() {
         assert!(!msg
             .flags
             .intersects(MsgFlags::MSG_TRUNC | MsgFlags::MSG_CTRUNC));
-        assert_eq!(msg.cmsgs().count(), 2, "expected 2 cmsgs");
+        assert_eq!(msg.cmsgs().unwrap().count(), 2, "expected 2 cmsgs");
 
         let mut rx_recvif = false;
         let mut rx_recvdstaddr = false;
-        for cmsg in msg.cmsgs() {
+        for cmsg in msg.cmsgs().unwrap() {
             match cmsg {
                 ControlMessageOwned::Ipv4RecvIf(dl) => {
                     rx_recvif = true;
@@ -2027,10 +2041,10 @@ pub fn test_recvif_ipv4() {
         assert!(!msg
             .flags
             .intersects(MsgFlags::MSG_TRUNC | MsgFlags::MSG_CTRUNC));
-        assert_eq!(msg.cmsgs().count(), 1, "expected 1 cmsgs");
+        assert_eq!(msg.cmsgs().unwrap().count(), 1, "expected 1 cmsgs");
 
         let mut rx_recvorigdstaddr = false;
-        for cmsg in msg.cmsgs() {
+        for cmsg in msg.cmsgs().unwrap() {
             match cmsg {
                 ControlMessageOwned::Ipv4OrigDstAddr(addr) => {
                     rx_recvorigdstaddr = true;
@@ -2113,10 +2127,10 @@ pub fn test_recvif_ipv6() {
         assert!(!msg
             .flags
             .intersects(MsgFlags::MSG_TRUNC | MsgFlags::MSG_CTRUNC));
-        assert_eq!(msg.cmsgs().count(), 1, "expected 1 cmsgs");
+        assert_eq!(msg.cmsgs().unwrap().count(), 1, "expected 1 cmsgs");
 
         let mut rx_recvorigdstaddr = false;
-        for cmsg in msg.cmsgs() {
+        for cmsg in msg.cmsgs().unwrap() {
             match cmsg {
                 ControlMessageOwned::Ipv6OrigDstAddr(addr) => {
                     rx_recvorigdstaddr = true;
@@ -2214,7 +2228,7 @@ pub fn test_recv_ipv6pktinfo() {
             .flags
             .intersects(MsgFlags::MSG_TRUNC | MsgFlags::MSG_CTRUNC));
 
-        let mut cmsgs = msg.cmsgs();
+        let mut cmsgs = msg.cmsgs().unwrap();
         if let Some(ControlMessageOwned::Ipv6PacketInfo(pktinfo)) = cmsgs.next()
         {
             let i = if_nametoindex(lo_name.as_bytes()).expect("if_nametoindex");
@@ -2357,7 +2371,7 @@ fn test_recvmsg_timestampns() {
         flags,
     )
     .unwrap();
-    let rtime = match r.cmsgs().next() {
+    let rtime = match r.cmsgs().unwrap().next() {
         Some(ControlMessageOwned::ScmTimestampns(rtime)) => rtime,
         Some(_) => panic!("Unexpected control message"),
         None => panic!("No control message"),
@@ -2418,7 +2432,7 @@ fn test_recvmmsg_timestampns() {
     )
     .unwrap()
     .collect();
-    let rtime = match r[0].cmsgs().next() {
+    let rtime = match r[0].cmsgs().unwrap().next() {
         Some(ControlMessageOwned::ScmTimestampns(rtime)) => rtime,
         Some(_) => panic!("Unexpected control message"),
         None => panic!("No control message"),
@@ -2508,7 +2522,7 @@ fn test_recvmsg_rxq_ovfl() {
                 MsgFlags::MSG_DONTWAIT,
             ) {
                 Ok(r) => {
-                    drop_counter = match r.cmsgs().next() {
+                    drop_counter = match r.cmsgs().unwrap().next() {
                         Some(ControlMessageOwned::RxqOvfl(drop_counter)) => {
                             drop_counter
                         }
@@ -2687,7 +2701,7 @@ mod linux_errqueue {
         assert_eq!(msg.address, Some(sock_addr));
 
         // Check for expected control message.
-        let ext_err = match msg.cmsgs().next() {
+        let ext_err = match msg.cmsgs().unwrap().next() {
             Some(cmsg) => testf(&cmsg),
             None => panic!("No control message"),
         };
@@ -2878,7 +2892,7 @@ fn test_recvmm2() -> nix::Result<()> {
         #[cfg(not(any(qemu, target_arch = "aarch64")))]
         let mut saw_time = false;
         let mut recvd = 0;
-        for cmsg in rmsg.cmsgs() {
+        for cmsg in rmsg.cmsgs().unwrap() {
             if let ControlMessageOwned::ScmTimestampsns(timestamps) = cmsg {
                 let ts = timestamps.system;