Commit 43c26a1a authored by Davide Caratti's avatar Davide Caratti Committed by David S. Miller
Browse files

net: more accurate checksumming in validate_xmit_skb() 



skb_csum_hwoffload_help() uses netdev features and skb->csum_not_inet to
determine if skb needs software computation of Internet Checksum or crc32c
(or nothing, if this computation can be done by the hardware). Use it in
place of skb_checksum_help() in validate_xmit_skb() to avoid corruption
of non-GSO SCTP packets having skb->ip_summed equal to CHECKSUM_PARTIAL.

While at it, remove references to skb_csum_off_chk* functions, since they
are not present anymore in Linux  _ see commit cf53b1da ("Revert
 "net: Add driver helper functions to determine checksum offloadability"").

Signed-off-by: default avatarDavide Caratti <dcaratti@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent dba00306

Documentation/networking/checksum-offloads.txt

+7 −4
Original line number Diff line number Diff line
@@ -35,6 +35,9 @@ This interface only allows a single checksum to be offloaded. Where 
 encapsulation is used, the packet may have multiple checksum fields in

 different header layers, and the rest will have to be handled by another

 mechanism such as LCO or RCO.

CRC32c can also be offloaded using this interface, by means of filling

 skb->csum_start and skb->csum_offset as described above, and setting

 skb->csum_not_inet: see skbuff.h comment (section 'D') for more details.

No offloading of the IP header checksum is performed; it is always done in

 software.  This is OK because when we build the IP header, we obviously

 have it in cache, so summing it isn't expensive.  It's also rather short.
@@ -49,9 +52,9 @@ A driver declares its offload capabilities in netdev->hw_features; see 
 and csum_offset given in the SKB; if it tries to deduce these itself in

 hardware (as some NICs do) the driver should check that the values in the

 SKB match those which the hardware will deduce, and if not, fall back to

 checksumming in software instead (with skb_checksum_help or one of the

 skb_csum_off_chk* functions as mentioned in include/linux/skbuff.h).  This

 is a pain, but that's what you get when hardware tries to be clever.

 checksumming in software instead (with skb_csum_hwoffload_help() or one of

 the skb_checksum_help() / skb_crc32c_csum_help functions, as mentioned in

 include/linux/skbuff.h).



The stack should, for the most part, assume that checksum offload is

 supported by the underlying device.  The only place that should check is
@@ -60,7 +63,7 @@ The stack should, for the most part, assume that checksum offload is 
 may include other offloads besides TX Checksum Offload) and, if they are

 not supported or enabled on the device (determined by netdev->features),

 performs the corresponding offload in software.  In the case of TX

 Checksum Offload, that means calling skb_checksum_help(skb).

 Checksum Offload, that means calling skb_csum_hwoffload_help(skb, features).





LCO: Local Checksum Offload

include/linux/netdevice.h

+3 −0
Original line number Diff line number Diff line
@@ -3930,6 +3930,9 @@ void netdev_rss_key_fill(void *buffer, size_t len); 
int dev_get_nest_level(struct net_device *dev);

int skb_checksum_help(struct sk_buff *skb);

int skb_crc32c_csum_help(struct sk_buff *skb);

int skb_csum_hwoffload_help(struct sk_buff *skb,

			    const netdev_features_t features);



struct sk_buff *__skb_gso_segment(struct sk_buff *skb,

				  netdev_features_t features, bool tx_path);

struct sk_buff *skb_mac_gso_segment(struct sk_buff *skb,

include/linux/skbuff.h

+5 −8
Original line number Diff line number Diff line
@@ -162,14 +162,11 @@ 
 *

 *   NETIF_F_IP_CSUM and NETIF_F_IPV6_CSUM are being deprecated in favor of

 *   NETIF_F_HW_CSUM. New devices should use NETIF_F_HW_CSUM to indicate

 *   checksum offload capability. If a	device has limited checksum capabilities

 *   (for instance can only perform NETIF_F_IP_CSUM or NETIF_F_IPV6_CSUM as

 *   described above) a helper function can be called to resolve

 *   CHECKSUM_PARTIAL. The helper functions are skb_csum_off_chk*. The helper

 *   function takes a spec argument that describes the protocol layer that is

 *   supported for checksum offload and can be called for each packet. If a

 *   packet does not match the specification for offload, skb_checksum_help

 *   is called to resolve the checksum.

 *   checksum offload capability.

 *   skb_csum_hwoffload_help() can be called to resolve CHECKSUM_PARTIAL based

 *   on network device checksumming capabilities: if a packet does not match

 *   them, skb_checksum_help or skb_crc32c_help (depending on the value of

 *   csum_not_inet, see item D.) is called to resolve the checksum.

 *

 * CHECKSUM_NONE:

 *

net/core/dev.c

+12 −2
Original line number Diff line number Diff line
@@ -2996,6 +2996,17 @@ static struct sk_buff *validate_xmit_vlan(struct sk_buff *skb, 
	return skb;

}



int skb_csum_hwoffload_help(struct sk_buff *skb,

			    const netdev_features_t features)

{

	if (unlikely(skb->csum_not_inet))

		return !!(features & NETIF_F_SCTP_CRC) ? 0 :

			skb_crc32c_csum_help(skb);



	return !!(features & NETIF_F_CSUM_MASK) ? 0 : skb_checksum_help(skb);

}

EXPORT_SYMBOL(skb_csum_hwoffload_help);



static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device *dev)

{

	netdev_features_t features;
@@ -3034,8 +3045,7 @@ static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device 
			else

				skb_set_transport_header(skb,

							 skb_checksum_start_offset(skb));

			if (!(features & NETIF_F_CSUM_MASK) &&

			    skb_checksum_help(skb))

			if (skb_csum_hwoffload_help(skb, features))

				goto out_kfree_skb;

		}

	}

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