Re: [lvc-project] [PATCH net v2] xsk: Fix overflow in descriptor validation

[Ilia Gavrilov <Ilia.Gavrilov@infotecs.ru>]

On 10/7/25 17:06, Ilia Gavrilov wrote:
> The desc->len value can be set up to U32_MAX. If umem tx_metadata_len
> option is also set, the value of the expression
> 'desc->len + pool->tx_metadata_len' can overflow and validation
> of the incorrect descriptor will be successfully passed.
> This can lead to a subsequent chain of arithmetic overflows
> in the xsk_build_skb() function and incorrect sk_buff allocation.
> 
> To reproduce the overflow, this piece of userspace code can be used:
>        struct xdp_umem_reg umem_reg;
>        umem_reg.addr = (__u64)(void *)umem;
>        ...
>        umem_reg.chunk_size = 4096;
>        umem_reg.tx_metadata_len = 16;
>        umem_reg.flags = XDP_UMEM_TX_METADATA_LEN;
>        setsockopt(sfd, SOL_XDP, XDP_UMEM_REG, &umem_reg, sizeof(umem_reg));
>        ...
> 
>        xsk_ring_prod__reserve(tq, batch_size, &idx);
> 
>        for (i = 0; i < nr_packets; ++i) {
>                struct xdp_desc *tx_desc = xsk_ring_prod__tx_desc(tq, idx + i);
>                tx_desc->addr = packets[i].addr;
>                tx_desc->addr += umem->tx_metadata_len;
>                tx_desc->options = XDP_TX_METADATA;
>                tx_desc->len = UINT32_MAX;
>        }
> 
>        xsk_ring_prod__submit(tq, nr_packets);
>        ...
>        sendto(sfd, NULL, 0, MSG_DONTWAIT, NULL, 0);
> 
> Found by InfoTeCS on behalf of Linux Verification Center
> (linuxtesting.org) with SVACE.
> 
> Fixes: 341ac980eab9 ("xsk: Support tx_metadata_len")
> Cc: stable@vger.kernel.org
> Signed-off-by: Ilia Gavrilov <Ilia.Gavrilov@infotecs.ru>
> ---
> v2: Add a repro
>  net/xdp/xsk_queue.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
> index f16f390370dc..b206a8839b39 100644
> --- a/net/xdp/xsk_queue.h
> +++ b/net/xdp/xsk_queue.h
> @@ -144,7 +144,7 @@ static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
>  					    struct xdp_desc *desc)
>  {
>  	u64 addr = desc->addr - pool->tx_metadata_len;
> -	u64 len = desc->len + pool->tx_metadata_len;
> +	u64 len = (u64)desc->len + pool->tx_metadata_len;
>  	u64 offset = addr & (pool->chunk_size - 1);
>  
>  	if (!desc->len)
> @@ -165,7 +165,7 @@ static inline bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool,
>  					      struct xdp_desc *desc)
>  {
>  	u64 addr = xp_unaligned_add_offset_to_addr(desc->addr) - pool->tx_metadata_len;
> -	u64 len = desc->len + pool->tx_metadata_len;
> +	u64 len = (u64)desc->len + pool->tx_metadata_len;
>  
>  	if (!desc->len)
>  		return false;

Hi, Alexander, Magnus!

I'm sorry to bother you.
Will this patch be applied or rejected?