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Fix corrupted sendmmsg() call #1414

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Apr 8, 2021
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2 changes: 2 additions & 0 deletions CHANGELOG.md
Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
### Fixed
- Allow `sockaddr_ll` size, as reported by the Linux kernel, to be smaller then it's definition
(#[1395](https://github.com/nix-rust/nix/pull/1395))
- Fix spurious errors using `sendmmsg` with multiple cmsgs
(#[1414](https://github.com/nix-rust/nix/pull/1414))

### Removed

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11 changes: 5 additions & 6 deletions src/sys/socket/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1101,23 +1101,22 @@ pub fn sendmmsg<'a, I, C>(

let mut output = Vec::<libc::mmsghdr>::with_capacity(reserve_items);

let mut cmsgs_buffer = vec![0u8; 0];
let mut cmsgs_buffers = Vec::<Vec<u8>>::with_capacity(reserve_items);

for d in iter {
let cmsgs_start = cmsgs_buffer.len();
let cmsgs_required_capacity: usize = d.cmsgs.as_ref().iter().map(|c| c.space()).sum();
let cmsgs_buffer_need_capacity = cmsgs_start + cmsgs_required_capacity;
cmsgs_buffer.resize(cmsgs_buffer_need_capacity, 0);
let capacity: usize = d.cmsgs.as_ref().iter().map(|c| c.space()).sum();
let mut cmsgs_buffer = vec![0u8; capacity];

output.push(libc::mmsghdr {
msg_hdr: pack_mhdr_to_send(
&mut cmsgs_buffer[cmsgs_start..],
&mut cmsgs_buffer,
&d.iov,
&d.cmsgs,
d.addr.as_ref()
),
msg_len: 0,
});
cmsgs_buffers.push(cmsgs_buffer);
};

let ret = unsafe { libc::sendmmsg(fd, output.as_mut_ptr(), output.len() as _, flags.bits() as _) };
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