Re: [PATCH v2 4/8] libmpathutil: vector_del_slot: modify v->allocated if realloc fails

[Benjamin Marzinski <bmarzins@redhat.com>]

On Wed, May 07, 2025 at 09:05:48PM +0200, Martin Wilck wrote:
> We use v->allocated with the semantics of "length" or "number of used
> elements" of a vector. If realloc() fails while deleting an element,
> we should keep the previously allocated v->slot array but still
> decrement "allocated" in order to avoid accessing invalid vector
> elements.
> 
> The next successful realloc will bring v->allocated and the actual
> size of the array in sync again.
> 
> Signed-off-by: Martin Wilck <mwilck@suse.com>

Reviewed-by: Benjamin Marzinski <bmarzins@redhat.com>

> ---
>  libmpathutil/vector.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/libmpathutil/vector.c b/libmpathutil/vector.c
> index 7f763cb..f69d644 100644
> --- a/libmpathutil/vector.c
> +++ b/libmpathutil/vector.c
> @@ -113,7 +113,7 @@ vector_del_slot(vector v, int slot)
>  		return;
>  
>  	for (i = slot + 1; i < VECTOR_SIZE(v); i++)
> -		v->slot[i-1] = v->slot[i];
> +		v->slot[i - 1] = v->slot[i];
>  
>  	v->allocated -= VECTOR_DEFAULT_SIZE;
>  
> @@ -125,9 +125,15 @@ vector_del_slot(vector v, int slot)
>  		void *new_slot;
>  
>  		new_slot = realloc(v->slot, sizeof (void *) * v->allocated);
> -		if (!new_slot)
> -			v->allocated += VECTOR_DEFAULT_SIZE;
> -		else
> +		/*
> +		 * If realloc() fails, v->allocated will be smaller than the
> +		 * actual allocated size vector size.
> +		 * This is intentional; we want VECTOR_SIZE() to return
> +		 * the number of used elements. Otherwise, vector_for_each_slot()
> +		 * et al. wouldn't work as intended; there might be duplicate
> +		 * or stale elements at the end of the vector.
> +		 */
> +		if (new_slot)
>  			v->slot = new_slot;
>  	}
>  }
> -- 
> 2.49.0