linux-kernel - Re: [RESEND PATCH] bcachefs: Annotate struct bucket_gens with __counted

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Message-ID: <ctariwoo6do3ergs4p7smzjbil7mwq744spzyzcphu2apwnkjn@hndqzlxejzvz>
Date: Sat, 26 Oct 2024 20:30:33 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Thorsten Blum <thorsten.blum@...ux.dev>
Cc: Kees Cook <kees@...nel.org>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org
Subject: Re: [RESEND PATCH] bcachefs: Annotate struct bucket_gens with
 __counted_by()

On Sat, Oct 26, 2024 at 05:47:04PM +0200, Thorsten Blum wrote:
> Add the __counted_by compiler attribute to the flexible array member b
> to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
> CONFIG_FORTIFY_SOURCE.
> 
> Use struct_size() to calculate the number of bytes to be allocated.
> 
> Update bucket_gens->nbuckets and bucket_gens->nbuckets_minus_first when
> resizing.
> 
> Compile-tested only.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>

I can take this patch without it being tested, but please have a look at
ktest:
https://evilpiepirate.org/git/ktest.git/

that's where all the bcachefs tests live, and it's a nice testing and
debugging tool. The CI runs the same tests, and I can give you an
account there as well.

> ---
>  fs/bcachefs/buckets.c       | 13 ++++++++-----
>  fs/bcachefs/buckets_types.h |  2 +-
>  2 files changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/bcachefs/buckets.c b/fs/bcachefs/buckets.c
> index ec7d9a59bea9..8bd17667e243 100644
> --- a/fs/bcachefs/buckets.c
> +++ b/fs/bcachefs/buckets.c
> @@ -1266,8 +1266,9 @@ int bch2_dev_buckets_resize(struct bch_fs *c, struct bch_dev *ca, u64 nbuckets)
>  
>  	BUG_ON(resize && ca->buckets_nouse);
>  
> -	if (!(bucket_gens	= kvmalloc(sizeof(struct bucket_gens) + nbuckets,
> -					   GFP_KERNEL|__GFP_ZERO))) {
> +	bucket_gens = kvmalloc(struct_size(bucket_gens, b, nbuckets),
> +			       GFP_KERNEL|__GFP_ZERO);
> +	if (!bucket_gens) {
>  		ret = -BCH_ERR_ENOMEM_bucket_gens;
>  		goto err;
>  	}
> @@ -1285,11 +1286,13 @@ int bch2_dev_buckets_resize(struct bch_fs *c, struct bch_dev *ca, u64 nbuckets)
>  	old_bucket_gens = rcu_dereference_protected(ca->bucket_gens, 1);
>  
>  	if (resize) {
> -		size_t n = min(bucket_gens->nbuckets, old_bucket_gens->nbuckets);
> -
> +		bucket_gens->nbuckets = min(bucket_gens->nbuckets,
> +					    old_bucket_gens->nbuckets);
> +		bucket_gens->nbuckets_minus_first =
> +			bucket_gens->nbuckets - bucket_gens->first_bucket;
>  		memcpy(bucket_gens->b,
>  		       old_bucket_gens->b,
> -		       n);
> +		       bucket_gens->nbuckets);
>  	}
>  
>  	rcu_assign_pointer(ca->bucket_gens, bucket_gens);
> diff --git a/fs/bcachefs/buckets_types.h b/fs/bcachefs/buckets_types.h
> index 28bd09a253c8..7174047b8e92 100644
> --- a/fs/bcachefs/buckets_types.h
> +++ b/fs/bcachefs/buckets_types.h
> @@ -24,7 +24,7 @@ struct bucket_gens {
>  	u16			first_bucket;
>  	size_t			nbuckets;
>  	size_t			nbuckets_minus_first;
> -	u8			b[];
> +	u8			b[] __counted_by(nbuckets);
>  };
>  
>  struct bch_dev_usage {
> -- 
> 2.47.0
>