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authorDaniel Borkmann <daniel@iogearbox.net>2016-08-05 00:11:12 +0200
committerDavid S. Miller <davem@davemloft.net>2016-08-08 13:11:43 -0700
commit479ffcccefd7b04442b0e949f8779b0612e8c75f (patch)
tree97d83930ebfdd05296018eec0c6bfe19f93b601b /include
parenta2bfe6bf09a5f38df2bd0b1734f5fdee76f9366f (diff)
bpf: fix checksum fixups on bpf_skb_store_bytes
bpf_skb_store_bytes() invocations above L2 header need BPF_F_RECOMPUTE_CSUM flag for updates, so that CHECKSUM_COMPLETE will be fixed up along the way. Where we ran into an issue with bpf_skb_store_bytes() is when we did a single-byte update on the IPv6 hoplimit despite using BPF_F_RECOMPUTE_CSUM flag; simple ping via ICMPv6 triggered a hw csum failure as a result. The underlying issue has been tracked down to a buffer alignment issue. Meaning, that csum_partial() computations via skb_postpull_rcsum() and skb_postpush_rcsum() pair invoked had a wrong result since they operated on an odd address for the hoplimit, while other computations were done on an even address. This mix doesn't work as-is with skb_postpull_rcsum(), skb_postpush_rcsum() pair as it always expects at least half-word alignment of input buffers, which is normally the case. Thus, instead of these helpers using csum_sub() and (implicitly) csum_add(), we need to use csum_block_sub(), csum_block_add(), respectively. For unaligned offsets, they rotate the sum to align it to a half-word boundary again, otherwise they work the same as csum_sub() and csum_add(). Adding __skb_postpull_rcsum(), __skb_postpush_rcsum() variants that take the offset as an input and adapting bpf_skb_store_bytes() to them fixes the hw csum failures again. The skb_postpull_rcsum(), skb_postpush_rcsum() helpers use a 0 constant for offset so that the compiler optimizes the offset & 1 test away and generates the same code as with csum_sub()/_add(). Fixes: 608cd71a9c7c ("tc: bpf: generalize pedit action") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include')
-rw-r--r--include/linux/skbuff.h52
1 files changed, 33 insertions, 19 deletions
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 6f0b3e0adc73..0f665cb26b50 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2847,6 +2847,18 @@ static inline int skb_linearize_cow(struct sk_buff *skb)
__skb_linearize(skb) : 0;
}
+static __always_inline void
+__skb_postpull_rcsum(struct sk_buff *skb, const void *start, unsigned int len,
+ unsigned int off)
+{
+ if (skb->ip_summed == CHECKSUM_COMPLETE)
+ skb->csum = csum_block_sub(skb->csum,
+ csum_partial(start, len, 0), off);
+ else if (skb->ip_summed == CHECKSUM_PARTIAL &&
+ skb_checksum_start_offset(skb) < 0)
+ skb->ip_summed = CHECKSUM_NONE;
+}
+
/**
* skb_postpull_rcsum - update checksum for received skb after pull
* @skb: buffer to update
@@ -2857,36 +2869,38 @@ static inline int skb_linearize_cow(struct sk_buff *skb)
* update the CHECKSUM_COMPLETE checksum, or set ip_summed to
* CHECKSUM_NONE so that it can be recomputed from scratch.
*/
-
static inline void skb_postpull_rcsum(struct sk_buff *skb,
const void *start, unsigned int len)
{
- if (skb->ip_summed == CHECKSUM_COMPLETE)
- skb->csum = csum_sub(skb->csum, csum_partial(start, len, 0));
- else if (skb->ip_summed == CHECKSUM_PARTIAL &&
- skb_checksum_start_offset(skb) < 0)
- skb->ip_summed = CHECKSUM_NONE;
+ __skb_postpull_rcsum(skb, start, len, 0);
}
-unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);
+static __always_inline void
+__skb_postpush_rcsum(struct sk_buff *skb, const void *start, unsigned int len,
+ unsigned int off)
+{
+ if (skb->ip_summed == CHECKSUM_COMPLETE)
+ skb->csum = csum_block_add(skb->csum,
+ csum_partial(start, len, 0), off);
+}
+/**
+ * skb_postpush_rcsum - update checksum for received skb after push
+ * @skb: buffer to update
+ * @start: start of data after push
+ * @len: length of data pushed
+ *
+ * After doing a push on a received packet, you need to call this to
+ * update the CHECKSUM_COMPLETE checksum.
+ */
static inline void skb_postpush_rcsum(struct sk_buff *skb,
const void *start, unsigned int len)
{
- /* For performing the reverse operation to skb_postpull_rcsum(),
- * we can instead of ...
- *
- * skb->csum = csum_add(skb->csum, csum_partial(start, len, 0));
- *
- * ... just use this equivalent version here to save a few
- * instructions. Feeding csum of 0 in csum_partial() and later
- * on adding skb->csum is equivalent to feed skb->csum in the
- * first place.
- */
- if (skb->ip_summed == CHECKSUM_COMPLETE)
- skb->csum = csum_partial(start, len, skb->csum);
+ __skb_postpush_rcsum(skb, start, len, 0);
}
+unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);
+
/**
* skb_push_rcsum - push skb and update receive checksum
* @skb: buffer to update