Shared memory `shmctl`: Permissions denied - linux

Question

I am trying to use shared memory in a process without using sudo.
My minimal example:
fn main() {
const KEY:i32 = 453845;
const SIZE:usize = 1024*1024;
unsafe {
let shmid = libc::shmget(KEY, SIZE, libc::IPC_CREAT);
dbg!(shmid);
dbg!(*libc::__errno_location());
let mut description: MaybeUninit<libc::shmid_ds> = MaybeUninit::uninit();
let result = libc::shmctl(KEY, libc::IPC_STAT, description.as_mut_ptr());
dbg!(description.assume_init_read());
dbg!(result);
dbg!(*libc::__errno_location());
}
}
produces the output:
[shared-memory-allocator/src/lib.rs:561] shmid = 1015817
[shared-memory-allocator/src/lib.rs:565] description.assume_init_read() = shmid_ds {
shm_perm: ipc_perm {
__key: 0,
uid: 0,
gid: 0,
cuid: 0,
cgid: 0,
mode: 0,
__pad1: 0,
__seq: 0,
__pad2: 0,
__unused1: 0,
__unused2: 0,
},
shm_segsz: 0,
shm_atime: 0,
shm_dtime: 0,
shm_ctime: 0,
shm_cpid: 0,
shm_lpid: 0,
shm_nattch: 0,
__unused4: 0,
__unused5: 0,
}
[shared-memory-allocator/src/lib.rs:566] result = -1
[shared-memory-allocator/src/lib.rs:567] *libc::__errno_location() = 22
Which is to note that it errors with error code 22 e.g. Permission Denied.
This seems like a simple use case, but checking https://linux.die.net/man/2/shmctl and https://linux.die.net/man/2/shmget has no description of permissions. Looking at https://www.ibm.com/docs/en/zos/2.1.0?topic=functions-shmget-get-shared-memory-segment it does note you can pass permission bits.
But if I change it to
let permissions = (libc::S_IRGRP | libc::S_IROTH | libc::S_IRUSR | libc::S_IWGRP | libc::S_IWOTH | libc::S_IWUSR) as i32;
let shmid = libc::shmget(KEY, SIZE, libc::IPC_CREAT | permissions);
The result is shmget now fails:
[shared-memory-allocator/src/lib.rs:562] shmid = -1
[shared-memory-allocator/src/lib.rs:563] *libc::__errno_location() = 13