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net_util: clean up transmutes in create_sockaddr()

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Rewrite create_sockaddr() using only safe type conversions instead of
the unsafe mem::transmute(), and add helper functions to do the sockaddr
to sockaddr_in (and vice versa) conversion safely.

BUG=b:365852007

Change-Id: I79690ebd1d10056800d46e8da1641ad44cb04b62
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/5760286
Reviewed-by: Dennis Kempin <denniskempin@google.com>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>
This commit is contained in:
Daniel Verkamp 2024-08-02 15:58:52 -07:00 committed by crosvm LUCI
parent 705a9a6465
commit 1457967c08
1 changed files with 36 additions and 11 deletions
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47
net_util/src/sys/linux/tap.rs
View file

@ -504,30 +504,55 @@ fn create_socket() -> Result<net::UdpSocket> {
Err(Error::CreateSocket(SysError::last()))
}
fn sockaddr_from_sockaddr_in(addr_in: libc::sockaddr_in) -> libc::sockaddr {
assert_eq!(
mem::size_of::<libc::sockaddr_in>(),
mem::size_of::<libc::sockaddr>()
);
// SAFETY: trivially safe
unsafe { mem::transmute::<libc::sockaddr_in, libc::sockaddr>(addr_in) }
}
fn sockaddr_in_from_sockaddr(addr: libc::sockaddr) -> Option<libc::sockaddr_in> {
if addr.sa_family as i32 != libc::AF_INET {
return None;
}
assert_eq!(
mem::size_of::<libc::sockaddr_in>(),
mem::size_of::<libc::sockaddr>()
);
// SAFETY:
// This is safe because sockaddr and sockaddr_in are the same size, and we've checked that
// this address is AF_INET.
Some(unsafe { mem::transmute::<libc::sockaddr, libc::sockaddr_in>(addr) })
}
/// Create a sockaddr_in from an IPv4 address, and expose it as
/// an opaque sockaddr suitable for usage by socket ioctls.
fn create_sockaddr(ip_addr: net::Ipv4Addr) -> libc::sockaddr {
// IPv4 addresses big-endian (network order), but Ipv4Addr will give us
// a view of those bytes directly so we can avoid any endian trickiness.
let addr_in = libc::sockaddr_in {
sin_family: libc::AF_INET as u16,
sin_port: 0,
// SAFETY: trivially safe
sin_addr: unsafe { mem::transmute(ip_addr.octets()) },
sin_addr: libc::in_addr {
// `Ipv4Addr::octets()` returns the address in network byte order, so use
// `from_be_bytes()` to convert it into the native endianness, then `to_be()` to convert
// it back into big-endian (network) byte order as required by `sockaddr_in`. This is
// effectively a no-op, and we could use `u32::from_ne_bytes()` instead, but it is
// easier to understand when written this way.
s_addr: u32::from_be_bytes(ip_addr.octets()).to_be(),
},
sin_zero: [0; 8usize],
};
// SAFETY: trivially safe
unsafe { mem::transmute(addr_in) }
sockaddr_from_sockaddr_in(addr_in)
}
/// Extract the IPv4 address from a sockaddr. Assumes the sockaddr is a sockaddr_in.
fn read_ipv4_addr(addr: &libc::sockaddr) -> net::Ipv4Addr {
debug_assert_eq!(addr.sa_family as i32, libc::AF_INET);
// SAFETY:
// This is safe because sockaddr and sockaddr_in are the same size, and we've checked that
// this address is AF_INET.
let in_addr: libc::sockaddr_in = unsafe { mem::transmute(*addr) };
let in_addr = sockaddr_in_from_sockaddr(*addr).unwrap();
net::Ipv4Addr::from(in_addr.sin_addr.s_addr)
}