Re: [PATCH] filelock: Fix fcntl/close race recovery compat path

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2024-07-23 at 17:03 +0200, Jann Horn wrote:
> When I wrote commit 3cad1bc01041 ("filelock: Remove locks reliably when
> fcntl/close race is detected"), I missed that there are two copies of the
> code I was patching: The normal version, and the version for 64-bit offsets
> on 32-bit kernels.
> Thanks to Greg KH for stumbling over this while doing the stable
> backport...
> 
> Apply exactly the same fix to the compat path for 32-bit kernels.
> 
> Fixes: c293621bbf67 ("[PATCH] stale POSIX lock handling")
> Cc: stable@kernel.org
> Link: https://bugs.chromium.org/p/project-zero/issues/detail?id=2563
> Signed-off-by: Jann Horn <jannh@google.com>
> ---
>  fs/locks.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index bdd94c32256f..9afb16e0683f 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -2570,8 +2570,9 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
>  	error = do_lock_file_wait(filp, cmd, file_lock);
>  
>  	/*
> -	 * Attempt to detect a close/fcntl race and recover by releasing the
> -	 * lock that was just acquired. There is no need to do that when we're
> +	 * Detect close/fcntl races and recover by zapping all POSIX locks
> +	 * associated with this file and our files_struct, just like on
> +	 * filp_flush(). There is no need to do that when we're
>  	 * unlocking though, or for OFD locks.
>  	 */
>  	if (!error && file_lock->c.flc_type != F_UNLCK &&
> @@ -2586,9 +2587,7 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
>  		f = files_lookup_fd_locked(files, fd);
>  		spin_unlock(&files->file_lock);
>  		if (f != filp) {
> -			file_lock->c.flc_type = F_UNLCK;
> -			error = do_lock_file_wait(filp, cmd, file_lock);
> -			WARN_ON_ONCE(error);
> +			locks_remove_posix(filp, files);
>  			error = -EBADF;
>  		}
>  	}
> 
> ---
> base-commit: 66ebbdfdeb093e097399b1883390079cd4c3022b
> change-id: 20240723-fs-lock-recover-compatfix-cf2cbab343d1

Doh! Good catch.

Reviewed-by: Jeff Layton <jlayton@kernel.org>