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sendmsg: Fix padding for ControlMessages, and zero it rather than leave it uninitialised #874

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sendmsg: Fix padding for ControlMessages, and zero it rather than leave it uninitialised #874

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46 changes: 32 additions & 14 deletions src/sys/socket/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -302,6 +302,18 @@ unsafe fn copy_bytes<'a, 'b, T: ?Sized>(src: &T, dst: &'a mut &'b mut [u8]) {
mem::swap(dst, &mut remainder);
}

/// Pad byte slice dst with `len` zeroes, and update the slice to point to
/// the remainder.
fn pad_bytes(len: usize, dst: &mut &mut [u8]) {
let mut tmpbuf = &mut [][..];
mem::swap(&mut tmpbuf, dst);
let (padding, mut remainder) = tmpbuf.split_at_mut(len);
for i in padding {
*i = 0;
}
mem::swap(dst, &mut remainder);
}

cfg_if! {
// Darwin and DragonFly BSD always align struct cmsghdr to 32-bit only.
if #[cfg(any(target_os = "dragonfly", target_os = "ios", target_os = "macos"))] {
Expand Down Expand Up @@ -559,13 +571,12 @@ impl<'a> ControlMessage<'a> {

let padlen = cmsg_align(mem::size_of_val(&cmsg)) -
mem::size_of_val(&cmsg);

let mut tmpbuf = &mut [][..];
mem::swap(&mut tmpbuf, buf);
let (_padding, mut remainder) = tmpbuf.split_at_mut(padlen);
mem::swap(buf, &mut remainder);
pad_bytes(padlen, buf);

copy_bytes(fds, buf);

let padlen = self.space() - self.len();
pad_bytes(padlen, buf);
},
ControlMessage::ScmTimestamp(t) => {
let cmsg = cmsghdr {
Expand All @@ -578,17 +589,24 @@ impl<'a> ControlMessage<'a> {

let padlen = cmsg_align(mem::size_of_val(&cmsg)) -
mem::size_of_val(&cmsg);

let mut tmpbuf = &mut [][..];
mem::swap(&mut tmpbuf, buf);
let (_padding, mut remainder) = tmpbuf.split_at_mut(padlen);
mem::swap(buf, &mut remainder);
pad_bytes(padlen, buf);

copy_bytes(t, buf);

let padlen = self.space() - self.len();
pad_bytes(padlen, buf);
},
ControlMessage::Unknown(UnknownCmsg(orig_cmsg, bytes)) => {
copy_bytes(orig_cmsg, buf);

let padlen = cmsg_align(mem::size_of_val(&orig_cmsg)) -
mem::size_of_val(&orig_cmsg);
pad_bytes(padlen, buf);

copy_bytes(bytes, buf);

let padlen = self.space() - self.len();
pad_bytes(padlen, buf);
}
}
}
Expand All @@ -601,24 +619,24 @@ impl<'a> ControlMessage<'a> {
///
/// Allocates if cmsgs is nonempty.
pub fn sendmsg<'a>(fd: RawFd, iov: &[IoVec<&'a [u8]>], cmsgs: &[ControlMessage<'a>], flags: MsgFlags, addr: Option<&'a SockAddr>) -> Result<usize> {
let mut len = 0;
let mut capacity = 0;
for cmsg in cmsgs {
len += cmsg.len();
capacity += cmsg.space();
}
// Note that the resulting vector claims to have length == capacity,
// so it's presently uninitialized.
let mut cmsg_buffer = unsafe {
let mut vec = Vec::<u8>::with_capacity(len);
vec.set_len(len);
let mut vec = Vec::<u8>::with_capacity(capacity);
vec.set_len(capacity);
vec
};
{
let end = unsafe{cmsg_buffer.as_ptr().offset(capacity as isize)};
let mut ptr = &mut cmsg_buffer[..];
for cmsg in cmsgs {
unsafe { cmsg.encode_into(&mut ptr) };
}
assert_eq!(ptr.as_ptr(), end);
}

let (name, namelen) = match addr {
Expand Down