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Message-Id: <200801280958.05130.rusty@rustcorp.com.au>
Date: Mon, 28 Jan 2008 09:58:04 +1100
From: Rusty Russell <rusty@...tcorp.com.au>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: netdev@...r.kernel.org
Subject: [PATCH] Implement skb_partial_csum_set
Implement skb_partial_csum_set, for setting partial csums on untrusted packets.
Use it in virtio_net (replacing buggy version there), it's also going
to be used by TAP for partial csum support.
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Acked-by: David S. Miller <davem@...emloft.net>
---
drivers/net/virtio_net.c | 11 +----------
include/linux/skbuff.h | 1 +
net/core/skbuff.c | 29 +++++++++++++++++++++++++++++
3 files changed, 31 insertions(+), 10 deletions(-)
diff -r 72be3d596d31 include/linux/skbuff.h
--- a/include/linux/skbuff.h Wed Jan 09 15:57:40 2008 +1100
+++ b/include/linux/skbuff.h Wed Jan 09 16:56:41 2008 +1100
@@ -1804,5 +1804,6 @@ static inline void skb_forward_csum(stru
skb->ip_summed = CHECKSUM_NONE;
}
+bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off);
#endif /* __KERNEL__ */
#endif /* _LINUX_SKBUFF_H */
diff -r 72be3d596d31 net/core/skbuff.c
--- a/net/core/skbuff.c Wed Jan 09 15:57:40 2008 +1100
+++ b/net/core/skbuff.c Wed Jan 09 16:56:41 2008 +1100
@@ -2214,6 +2214,34 @@ int skb_cow_data(struct sk_buff *skb, in
return elt;
}
+/**
+ * skb_partial_csum_set - set up and verify partial csum values for packet
+ * @skb: the skb to set
+ * @start: the number of bytes after skb->data to start checksumming.
+ * @off: the offset from start to place the checksum.
+ *
+ * For untrusted partially-checksummed packets, we need to make sure the values
+ * for skb->csum_start and skb->csum_offset are valid so we don't oops.
+ *
+ * This function checks and sets those values and skb->ip_summed: if this
+ * returns false you should drop the packet.
+ */
+bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off)
+{
+ if (unlikely(start > skb->len - 2) ||
+ unlikely((int)start + off > skb->len - 2)) {
+ if (net_ratelimit())
+ printk(KERN_WARNING
+ "bad partial csum: csum=%u/%u len=%u\n",
+ start, off, skb->len);
+ return false;
+ }
+ skb->ip_summed = CHECKSUM_PARTIAL;
+ skb->csum_start = skb_headroom(skb) + start;
+ skb->csum_offset = off;
+ return true;
+}
+
EXPORT_SYMBOL(___pskb_trim);
EXPORT_SYMBOL(__kfree_skb);
EXPORT_SYMBOL(kfree_skb);
@@ -2250,3 +2278,4 @@ EXPORT_SYMBOL(skb_append_datato_frags);
EXPORT_SYMBOL_GPL(skb_to_sgvec);
EXPORT_SYMBOL_GPL(skb_cow_data);
+EXPORT_SYMBOL_GPL(skb_partial_csum_set);
diff -r 72be3d596d31 drivers/net/virtio_net.c
--- a/drivers/net/virtio_net.c Wed Jan 09 15:57:40 2008 +1100
+++ b/drivers/net/virtio_net.c Wed Jan 09 16:56:41 2008 +1100
@@ -89,17 +89,8 @@ static void receive_skb(struct net_devic
if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
pr_debug("Needs csum!\n");
- skb->ip_summed = CHECKSUM_PARTIAL;
- skb->csum_start = hdr->csum_start;
- skb->csum_offset = hdr->csum_offset;
- if (skb->csum_start > skb->len - 2
- || skb->csum_offset > skb->len - 2) {
- if (net_ratelimit())
- printk(KERN_WARNING "%s: csum=%u/%u len=%u\n",
- dev->name, skb->csum_start,
- skb->csum_offset, skb->len);
+ if (!skb_partial_csum_set(skb,hdr->csum_start,hdr->csum_offset))
goto frame_err;
- }
}
if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
--
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