linux-kernel - Re: [PATCH 20/24] dm: only call early_lookup

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Message-ID: <ZGzw1c60WJBTNclC@redhat.com>
Date:   Tue, 23 May 2023 12:59:01 -0400
From:   Mike Snitzer <snitzer@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Joern Engel <joern@...ybastard.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Pavel Machek <pavel@....cz>, dm-devel@...hat.com,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-mtd@...ts.infradead.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 20/24] dm: only call early_lookup_bdev from early boot
 context

On Tue, May 23 2023 at  3:45P -0400,
Christoph Hellwig <hch@....de> wrote:

> early_lookup_bdev is supposed to only be called from the early boot
> code, but dm_get_device calls it as a general fallback when lookup_bdev
> fails, which is problematic because early_lookup_bdev bypasses all normal
> path based permission checking, and might cause problems with certain
> container environments renaming devices.
> 
> Switch to only call early_lookup_bdev when dm is built-in and the system
> state in not running yet.  This means it is still available when tables
> are constructed by dm-init.c from the kernel command line, but not
> otherwise.
> 
> Note that this strictly speaking changes the kernel ABI as the PARTUUID=
> and PARTLABEL= style syntax is now not available during a running
> systems.  They never were intended for that, but this breaks things
> we'll have to figure out a way to make them available again.  But if
> avoidable in any way I'd rather avoid that.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/md/dm-table.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index e997f4322a9967..c230241a76b374 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -326,8 +326,11 @@ static int upgrade_mode(struct dm_dev_internal *dd, fmode_t new_mode,
>  /*
>   * Add a device to the list, or just increment the usage count if
>   * it's already present.
> + *
> + * Note: the __ref annotation is because this function can call the __init
> + * marked early_lookup_bdev when called during early boot code from dm-init.c.
>   */
> -int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
> +int __ref dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
>  		  struct dm_dev **result)
>  {
>  	int r;
> @@ -346,8 +349,10 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
>  			return -EOVERFLOW;
>  	} else {
>  		r = lookup_bdev(path, &dev);
> -		if (r)
> +#ifndef MODULE
> +		if (r && system_state < SYSTEM_RUNNING)
>  			r = early_lookup_bdev(path, &dev);
> +#endif
>  		if (r)
>  			return -ENODEV;
>  	}
> -- 
> 2.39.2
> 

I think/hope this will be fine:

Reviewed-by: Mike Snitzer <snitzer@...nel.org>