linux-kernel - Re: [PATCH] ubifs: Correctly handle 0 value hashes in ubifs

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Date:   Mon, 24 Apr 2017 23:41:38 +0200
From:   Richard Weinberger <richard@....at>
To:     linux-mtd@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        david@...ma-star.at, stable@...r.kernel.org
Subject: Re: [PATCH] ubifs: Correctly handle 0 value hashes in ubifs_lookup()

Am 24.04.2017 um 23:31 schrieb Richard Weinberger:
> Use fname_name(&nm) == NULL to detect whether a double hash
> lookup should be performed instead of checking for nm.hash
> being non-zero. zero is a valid hash value.
> 
> Fixes: f4f61d2cc6d8 ("ubifs: Implement encrypted filenames")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Richard Weinberger <richard@....at>
> ---
>  fs/ubifs/dir.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c
> index b777bddaa1dd..ff77a0aa2f2b 100644
> --- a/fs/ubifs/dir.c
> +++ b/fs/ubifs/dir.c
> @@ -249,9 +249,8 @@ static struct dentry *ubifs_lookup(struct inode *dir, struct dentry *dentry,
>  		goto out_fname;
>  	}
>  
> -	if (nm.hash) {
> +	if (fname_name(&nm) == NULL) {
>  		ubifs_assert(fname_len(&nm) == 0);
> -		ubifs_assert(fname_name(&nm) == NULL);
>  		dent_key_init_hash(c, &key, dir->i_ino, nm.hash);
>  		err = ubifs_tnc_lookup_dh(c, &key, dent, nm.minor_hash);
>  	} else {
> 

Just realized that checking for nm.hash being non-zero is still legit on UBIFS
since UBIFS uses hash values 0, 1 and 2 in readdir() as special values.
key_mask_hash() makes sure that no hash value is smaller than 3 that goes do disk.

Thanks,
//richard