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wayland: Seal memfd to prevent shrinking

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I believe this should be possible wherever `memfd_create` is available.

Sealing isn't required, but Wayland doesn't allow a client to shrink an
shm pool, so there's no reason we should shrink the file. And if we mmap
the file, this prevents a `SIGBUS` if the compositor (incorrectly)
shrunk it.

So we might as well do this.
This commit is contained in:
Ian Douglas Scott 2023-01-05 17:23:19 -08:00
parent 2cdbb48b8c
commit 165a15e92c
1 changed files with 14 additions and 3 deletions
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17
src/wayland/buffer.rs
View file

@ -16,11 +16,22 @@ use super::State;
#[cfg(any(target_os = "linux", target_os = "freebsd"))] #[cfg(any(target_os = "linux", target_os = "freebsd"))]
fn create_memfile() -> File { fn create_memfile() -> File {
use nix::sys::memfd::{memfd_create, MemFdCreateFlag}; use nix::{
fcntl::{fcntl, FcntlArg, SealFlag},
sys::memfd::{memfd_create, MemFdCreateFlag},
};
let name = unsafe { CStr::from_bytes_with_nul_unchecked("softbuffer\0".as_bytes()) }; let name = unsafe { CStr::from_bytes_with_nul_unchecked("softbuffer\0".as_bytes()) };
let fd = memfd_create(name, MemFdCreateFlag::MFD_CLOEXEC) let fd = memfd_create(
.expect("Failed to create memfd to store buffer."); name,
MemFdCreateFlag::MFD_CLOEXEC | MemFdCreateFlag::MFD_ALLOW_SEALING,
)
.expect("Failed to create memfd to store buffer.");
let _ = fcntl(
fd,
FcntlArg::F_ADD_SEALS(SealFlag::F_SEAL_SHRINK | SealFlag::F_SEAL_SEAL),
)
.expect("Failed to seal memfd.");
unsafe { File::from_raw_fd(fd) } unsafe { File::from_raw_fd(fd) }
} }