RE: [PATCH net v2] net: qualcomm: rmnet: validate MAP frame length before ingress parsing

[<subash.a.kasiviswanathan@oss.qualcomm.com>]

> -----Original Message-----
> From: Xiang Mei <xmei5@asu.edu>
> Sent: Tuesday, June 30, 2026 11:41 AM
> To: subash.a.kasiviswanathan@oss.qualcomm.com;
> sean.tranchetti@oss.qualcomm.com; netdev@vger.kernel.org
> Cc: andrew+netdev@lunn.ch; davem@davemloft.net;
> edumazet@google.com; kuba@kernel.org; pabeni@redhat.com; linux-
> kernel@vger.kernel.org; bestswngs@gmail.com; Xiang Mei <xmei5@asu.edu>
> Subject: [PATCH net v2] net: qualcomm: rmnet: validate MAP frame length
> before ingress parsing
> 
> When ingress deaggregation is disabled, rmnet_map_ingress_handler() passes
> the skb straight to __rmnet_map_ingress_handler(), skipping the length
> validation that rmnet_map_deaggregate() performs on the aggregated path.
> The parser then dereferences the MAP header and csum header/trailer based
> on
> the on-wire pkt_len without checking skb->len, so a short frame is read
out
> of bounds:
> 
>   BUG: KASAN: slab-out-of-bounds in
> rmnet_map_checksum_downlink_packet
>   Read of size 1 at addr ffff88801118ed00 by task exploit/147
>   Call Trace:
>    ...
>    rmnet_map_checksum_downlink_packet
> (drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c:413)
>    __rmnet_map_ingress_handler
> (drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c:96)
>    rmnet_rx_handler
> (drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c:129)
>    __netif_receive_skb_core.constprop.0 (net/core/dev.c:6089)
>    netif_receive_skb (net/core/dev.c:6460)
>    tun_get_user (drivers/net/tun.c:1955)
>    tun_chr_write_iter (drivers/net/tun.c:2001)
>    vfs_write (fs/read_write.c:688)
>    ksys_write (fs/read_write.c:740)
>    do_syscall_64 (arch/x86/entry/syscall_64.c:94)
>    ...
> 
> Factor that validation out of rmnet_map_deaggregate() into
> rmnet_map_validate_packet_len() and run it on the no-aggregation path too.
> The MAP header is bounds-checked first, since this path can receive a
frame
> shorter than the header.
> 
> Fixes: ceed73a2cf4a ("drivers: net: ethernet: qualcomm: rmnet: Initial
> implementation")
> Reported-by: Weiming Shi <bestswngs@gmail.com>
> Suggested-by: Subash Abhinov Kasiviswanathan
> <subash.a.kasiviswanathan@oss.qualcomm.com>
> Signed-off-by: Xiang Mei <xmei5@asu.edu>
> ---
> v2: Validate on the no-aggregation path by reusing the deaggregation
>     length checks (factored into rmnet_map_validate_packet_len()) instead
>     of adding separate pskb_may_pull() guards in
> __rmnet_map_ingress_handler().
> 
>  .../ethernet/qualcomm/rmnet/rmnet_handlers.c  |  5 +-
>  .../net/ethernet/qualcomm/rmnet/rmnet_map.h   |  1 +
>  .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 72 ++++++++++---------
>  3 files changed, 45 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> index 9f3479500f85..d055a2628d8c 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> @@ -126,7 +126,10 @@ rmnet_map_ingress_handler(struct sk_buff *skb,
> 
>  		consume_skb(skb);
>  	} else {
> -		__rmnet_map_ingress_handler(skb, port);
> +		if (rmnet_map_validate_packet_len(skb, port))
> +			__rmnet_map_ingress_handler(skb, port);
> +		else
> +			kfree_skb(skb);
>  	}
>  }
> 
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> index b70284095568..60ca8b780c88 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
> @@ -59,5 +59,6 @@ void rmnet_map_tx_aggregate_init(struct rmnet_port
> *port);
>  void rmnet_map_tx_aggregate_exit(struct rmnet_port *port);
>  void rmnet_map_update_ul_agg_config(struct rmnet_port *port, u32 size,
>  				    u32 count, u32 time);
> +u32 rmnet_map_validate_packet_len(struct sk_buff *skb, struct rmnet_port
> *port);
> 
>  #endif /* _RMNET_MAP_H_ */
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> index 8b4640c5d61e..305ae15ae8f3 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> @@ -333,54 +333,62 @@ struct rmnet_map_header
> *rmnet_map_add_map_header(struct sk_buff *skb,
>  	return map_header;
>  }
> 
> -/* Deaggregates a single packet
> - * A whole new buffer is allocated for each portion of an aggregated
frame.
> - * Caller should keep calling deaggregate() on the source skb until 0 is
> - * returned, indicating that there are no more packets to deaggregate.
Caller
> - * is responsible for freeing the original skb.
> - */
> -struct sk_buff *rmnet_map_deaggregate(struct sk_buff *skb,
> -				      struct rmnet_port *port)
> +u32 rmnet_map_validate_packet_len(struct sk_buff *skb, struct rmnet_port
> *port)
>  {
>  	struct rmnet_map_v5_csum_header *next_hdr = NULL;
>  	struct rmnet_map_header *maph;
>  	void *data = skb->data;
> -	struct sk_buff *skbn;
> -	u8 nexthdr_type;
>  	u32 packet_len;
> 
> -	if (skb->len == 0)
> -		return NULL;
> +	if (skb->len < sizeof(*maph))
> +		return 0;
> 
>  	maph = (struct rmnet_map_header *)skb->data;
> +
> +	/* Some hardware can send us empty frames. Catch them */
> +	if (!maph->pkt_len)
> +		return 0;
> +
>  	packet_len = ntohs(maph->pkt_len) + sizeof(*maph);
> 
>  	if (port->data_format & RMNET_FLAGS_INGRESS_MAP_CKSUMV4) {
>  		packet_len += sizeof(struct rmnet_map_dl_csum_trailer);
> -	} else if (port->data_format &
> RMNET_FLAGS_INGRESS_MAP_CKSUMV5) {
> -		if (!(maph->flags & MAP_CMD_FLAG)) {
> -			packet_len += sizeof(*next_hdr);
> -			if (maph->flags & MAP_NEXT_HEADER_FLAG)
> -				next_hdr = data + sizeof(*maph);
> -			else
> -				/* Mapv5 data pkt without csum hdr is
invalid
> */
> -				return NULL;
> -		}
> +	} else if ((port->data_format &
> RMNET_FLAGS_INGRESS_MAP_CKSUMV5) &&
> +		   !(maph->flags & MAP_CMD_FLAG)) {
> +		/* Mapv5 data pkt without csum hdr is invalid */
> +		if (!(maph->flags & MAP_NEXT_HEADER_FLAG))
> +			return 0;
> +
> +		packet_len += sizeof(*next_hdr);
> +		next_hdr = data + sizeof(*maph);
>  	}
> 
> -	if (((int)skb->len - (int)packet_len) < 0)
> -		return NULL;
> +	if (skb->len < packet_len)
> +		return 0;
> 
> -	/* Some hardware can send us empty frames. Catch them */
> -	if (!maph->pkt_len)
> -		return NULL;
> +	if (next_hdr &&
> +	    u8_get_bits(next_hdr->header_info,
> MAPV5_HDRINFO_HDR_TYPE_FMASK) !=
> +	    RMNET_MAP_HEADER_TYPE_CSUM_OFFLOAD)
> +		return 0;
> 
> -	if (next_hdr) {
> -		nexthdr_type = u8_get_bits(next_hdr->header_info,
> -
> MAPV5_HDRINFO_HDR_TYPE_FMASK);
> -		if (nexthdr_type !=
> RMNET_MAP_HEADER_TYPE_CSUM_OFFLOAD)
> -			return NULL;
> -	}
> +	return packet_len;
> +}
> +
> +/* Deaggregates a single packet
> + * A whole new buffer is allocated for each portion of an aggregated
frame.
> + * Caller should keep calling deaggregate() on the source skb until 0 is
> + * returned, indicating that there are no more packets to deaggregate.
Caller
> + * is responsible for freeing the original skb.
> + */
> +struct sk_buff *rmnet_map_deaggregate(struct sk_buff *skb,
> +				      struct rmnet_port *port)
> +{
> +	struct sk_buff *skbn;
> +	u32 packet_len;
> +
> +	packet_len = rmnet_map_validate_packet_len(skb, port);
> +	if (!packet_len)
> +		return NULL;
> 
>  	skbn = alloc_skb(packet_len + RMNET_MAP_DEAGGR_SPACING,
> GFP_ATOMIC);
>  	if (!skbn)
> --
> 2.43.0

Reviewed-by: Subash Abhinov Kasiviswanathan
<subash.a.kasiviswanathan@oss.qualcomm.com>