Re: [PATCH 03/27] repair: refactor the BLKMAP_NEXTS_MAX check

[Dave Chinner <david@fromorbit.com>]

On Mon, Jan 29, 2024 at 08:31:51AM +0100, Christoph Hellwig wrote:
> Check the 32-bit limits using sizeof instead of cpp ifdefs so that we
> can get rid of BITS_PER_LONG.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  repair/bmap.c | 23 +++++++++++++++--------
>  repair/bmap.h | 13 -------------
>  2 files changed, 15 insertions(+), 21 deletions(-)
> 
> diff --git a/repair/bmap.c b/repair/bmap.c
> index cd1a8b07b..d1b2faaec 100644
> --- a/repair/bmap.c
> +++ b/repair/bmap.c
> @@ -22,6 +22,15 @@
>  pthread_key_t	dblkmap_key;
>  pthread_key_t	ablkmap_key;
>  
> +/*
> + * For 32 bit platforms, we are limited to extent arrays of 2^31 bytes, which
> + * limits the number of extents in an inode we can check. If we don't limit the
> + * valid range, we can overflow the BLKMAP_SIZE() calculation and allocate less
> + * memory than we think we needed, and hence walk off the end of the array and
> + * corrupt memory.
> + */
> +#define BLKMAP_NEXTS32_MAX	((INT_MAX / sizeof(bmap_ext_t)) - 1)
> +
>  blkmap_t *
>  blkmap_alloc(
>  	xfs_extnum_t	nex,
> @@ -35,8 +44,7 @@ blkmap_alloc(
>  	if (nex < 1)
>  		nex = 1;
>  
> -#if (BITS_PER_LONG == 32)	/* on 64-bit platforms this is never true */
> -	if (nex > BLKMAP_NEXTS_MAX) {
> +	if (sizeof(long) == 32 && nex > BLKMAP_NEXTS32_MAX) {

That's a really, really big long. sizeof(long) = 4, perhaps?

-Dave.
-- 
Dave Chinner
david@fromorbit.com