From 479ffcccefd7b04442b0e949f8779b0612e8c75f Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Fri, 5 Aug 2016 00:11:12 +0200 Subject: 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 Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- net/core/filter.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'net') diff --git a/net/core/filter.c b/net/core/filter.c index c46244f..5ecd5c9 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -1401,7 +1401,7 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags) return -EFAULT; if (flags & BPF_F_RECOMPUTE_CSUM) - skb_postpull_rcsum(skb, ptr, len); + __skb_postpull_rcsum(skb, ptr, len, offset); memcpy(ptr, from, len); @@ -1410,7 +1410,7 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags) skb_store_bits(skb, offset, ptr, len); if (flags & BPF_F_RECOMPUTE_CSUM) - skb_postpush_rcsum(skb, ptr, len); + __skb_postpush_rcsum(skb, ptr, len, offset); if (flags & BPF_F_INVALIDATE_HASH) skb_clear_hash(skb); -- cgit v1.1