Re: [PATCH] bcachefs: zero-init move_bucket struct in bch2_copygc_get_buckets()

[Kent Overstreet]

On Mon, Nov 11, 2024 at 03:42:44PM +0100, Gianfranco Trad wrote:
> zero-init move_bucket struct b fields in bch2_copygc_get_buckets() 
> to mitigate later uninit-value-use KMSAN reported bug.
> 
> Reported-by: syzbot+8689d10f1894eedf774d@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=8689d10f1894eedf774d
> Tested-by: syzbot+8689d10f1894eedf774d@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Gianfranco Trad <gianf.trad@xxxxxxxxx>
> ---
>  fs/bcachefs/movinggc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/bcachefs/movinggc.c b/fs/bcachefs/movinggc.c
> index d658be90f737..cdc456b03bec 100644
> --- a/fs/bcachefs/movinggc.c
> +++ b/fs/bcachefs/movinggc.c
> @@ -171,7 +171,8 @@ static int bch2_copygc_get_buckets(struct moving_context *ctxt,
>  				  lru_pos(BCH_LRU_FRAGMENTATION_START, 0, 0),
>  				  lru_pos(BCH_LRU_FRAGMENTATION_START, U64_MAX, LRU_TIME_MAX),
>  				  0, k, ({
> -		struct move_bucket b = { .k.bucket = u64_to_bucket(k.k->p.offset) };
> +		struct move_bucket b = { 0 };
> +		b.k.bucket = u64_to_bucket(k.k->p.offset);
>  		int ret2 = 0;

Providing any sort of initializer should cause the whole struct to be
initialized, are you and syzbot sure this is the right fix?