linux-kernel - Re: [PATCH 1/2] vboxsf: Avoid an spurious warning if load_nls

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Message-ID: <ZUOWS6Vr0rg4VVIb@casper.infradead.org>
Date:   Thu, 2 Nov 2023 12:30:03 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Hans de Goede <hdegoede@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/2] vboxsf: Avoid an spurious warning if load_nls_xxx()
 fails

On Wed, Nov 01, 2023 at 11:49:48AM +0100, Christophe JAILLET wrote:
> If an load_nls_xxx() function fails a few lines above, the 'sbi->bdi_id' is
> still 0.
> So, in the error handling path, we will call ida_simple_remove(..., 0)
> which is not allocated yet.
> 
> In order to prevent a spurious "ida_free called for id=0 which is not
> allocated." message, tweak the error handling path and add a new label.

That's not spurious!  You're freeing something that wasn't allocated.
A good quality malloc allocation will warn you if you free() a random
pointer.  I agree with everything abuot this patch (and the next) except
for the changelog.

> Fixes: 0fd169576648 ("fs: Add VirtualBox guest shared folder (vboxsf) support")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>  fs/vboxsf/super.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/vboxsf/super.c b/fs/vboxsf/super.c
> index 1fb8f4df60cb..9848af78215b 100644
> --- a/fs/vboxsf/super.c
> +++ b/fs/vboxsf/super.c
> @@ -151,7 +151,7 @@ static int vboxsf_fill_super(struct super_block *sb, struct fs_context *fc)
>  		if (!sbi->nls) {
>  			vbg_err("vboxsf: Count not load '%s' nls\n", nls_name);
>  			err = -EINVAL;
> -			goto fail_free;
> +			goto fail_destroy_idr;
>  		}
>  	}
>  
> @@ -224,6 +224,7 @@ static int vboxsf_fill_super(struct super_block *sb, struct fs_context *fc)
>  		ida_simple_remove(&vboxsf_bdi_ida, sbi->bdi_id);
>  	if (sbi->nls)
>  		unload_nls(sbi->nls);
> +fail_destroy_idr:
>  	idr_destroy(&sbi->ino_idr);
>  	kfree(sbi);
>  	return err;
> -- 
> 2.34.1
> 
>