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fix(vmnet): skip zero-length buffers #375

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Merged
Lencerf merged 1 commit into from
Jan 25, 2026
Merged

fix(vmnet): skip zero-length buffers #375

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74 changes: 29 additions & 45 deletions alioth/src/virtio/dev/net/vmnet.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -404,28 +404,7 @@ impl VirtioMio for Net {

fn read_from_vmnet(interface: *mut VmnetInterface) -> impl FnMut(&mut DescChain) -> Result<Status> {
move |chain: &mut DescChain| {
let mut trim_len = size_of::<VirtioNetHdr>();
let mut iov = Vec::with_capacity(chain.writable.len());

for buf in chain.writable.iter_mut() {
if trim_len > 0 {
if let Some((_, tail)) = buf.split_at_mut_checked(trim_len) {
iov.push(libc::iovec {
iov_base: tail.as_ptr() as *mut c_void,
iov_len: tail.len(),
});
trim_len = 0;
} else {
trim_len -= buf.len();
}
} else {
iov.push(libc::iovec {
iov_base: buf.as_ptr() as *mut c_void,
iov_len: buf.len(),
});
}
}

let mut iov = trim_desc_chain(chain.writable.iter().map(|b| &**b));
let size = iov.iter().map(|s| s.iov_len).sum();
let mut packets = VmPktDesc {
vm_pkt_size: size,
Expand Down Expand Up @@ -455,32 +434,11 @@ fn read_from_vmnet(interface: *mut VmnetInterface) -> impl FnMut(&mut DescChain)

fn write_to_vmnet(interface: *mut VmnetInterface) -> impl FnMut(&mut DescChain) -> Result<Status> {
move |chain: &mut DescChain| {
let mut trim_len = size_of::<VirtioNetHdr>();
let mut iov = Vec::with_capacity(chain.readable.len());

for buf in chain.readable.iter() {
if trim_len > 0 {
if let Some((_, tail)) = buf.split_at_checked(trim_len) {
iov.push(libc::iovec {
iov_base: tail.as_ptr() as *mut c_void,
iov_len: tail.len(),
});
trim_len = 0;
} else {
trim_len -= buf.len();
}
} else {
iov.push(libc::iovec {
iov_base: buf.as_ptr() as *mut c_void,
iov_len: buf.len(),
});
}
}

let mut iov = trim_desc_chain(chain.readable.iter().map(|b| &**b));
let size = iov.iter().map(|s| s.iov_len).sum();
let mut packets = VmPktDesc {
vm_pkt_size: size,
vm_pkt_iov: iov.as_ptr() as *mut libc::iovec,
vm_pkt_iov: iov.as_mut_ptr(),
vm_pkt_iovcnt: iov.len() as u32,
vm_flags: 0,
};
Expand Down Expand Up @@ -508,3 +466,29 @@ impl DevParam for NetVmnetParam {
Net::new(self, name)
}
}

fn trim_desc_chain<'m>(bufs: impl Iterator<Item = &'m [u8]>) -> Vec<libc::iovec> {
let mut iov = Vec::new();
let mut trim_len = size_of::<VirtioNetHdr>();

for buf in bufs {
let b = if trim_len > 0 {
if let Some((_, tail)) = buf.split_at_checked(trim_len)
&& !tail.is_empty()
{
trim_len = 0;
tail
} else {
trim_len -= buf.len();
continue;
}
} else {
buf
};
iov.push(libc::iovec {
iov_base: b.as_ptr() as *mut c_void,
iov_len: b.len(),
});
}
iov
}