linux-kernel - Re: [RFC PATCH 1/1] ipc, sem: fix backward compatibility with x86-32 kernels

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Date:   Mon, 16 May 2022 14:06:20 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Maxim Zhukov <crazycdeveloper@...il.com>
Cc:     chi.minghao@....com.cn, varad.gautam@...e.com, arnd@...db.de,
        shakeelb@...gle.com, vasily.averin@...ux.dev,
        manfred@...orfullife.com, dbueso@...e.de,
        linux-kernel@...r.kernel.org,
        Maxim Zhukov <mussitantesmortem@...il.com>
Subject: Re: [RFC PATCH 1/1] ipc, sem: fix backward compatibility with
 x86-32 kernels

On Sun, 15 May 2022 23:01:03 +0300 Maxim Zhukov <crazycdeveloper@...il.com> wrote:

> Since with commit 275f22148e87 ("ipc: rename old-style shmctl/semctl/msgctl syscalls")
> we have changed behavior:
> 
> ksys_semctl lost parse ipc version (ipc_parse_version), because the
> new syscall works with IPC_64 only, but the parse function has some
> side effect - it removes IPC_64 bit from `cmd`.
> 
> Some libc forced sends IPC_64 bit in semctl syscall[1][2][3], this leads to
> a bug - X86-32 kernel does not have compat headers and does not
> correctly parse received command (cmd) from semctl syscall: cmd have actual
> command and IPC_64 bit, thus throw EINVAL error in ksys_semctl
> 
> This commit forcibly removes IPC_64 bit from the cmd for restore
> backward compatibility.
> 
> [1]: https://elixir.bootlin.com/uclibc-ng/v1.0.40/source/libc/misc/sysvipc/sem.c#L58
> [2]: https://elixir.bootlin.com/musl/v1.2.3/source/src/ipc/semctl.c#L48 -> https://elixir.bootlin.com/musl/v1.2.3/source/src/ipc/ipc.h#L22
> [3]: https://elixir.bootlin.com/glibc/glibc-2.35/source/sysdeps/unix/sysv/linux/semctl.c#L124
> 

Thanks.

275f22148e87 was three years ago.  Can you suggest why it took so long
for this to be discovered?