Messages in this thread Patch in this message | | | From | Sasha Levin <> | Subject | [PATCH AUTOSEL 4.9 12/13] net: fix pskb_trim_rcsum_slow() with odd trim offset | Date | Tue, 30 Oct 2018 09:29:22 -0400 |
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From: Dimitris Michailidis <dmichail@google.com>
[ Upstream commit d55bef5059dd057bd077155375c581b49d25be7e ]
We've been getting checksum errors involving small UDP packets, usually 59B packets with 1 extra non-zero padding byte. netdev_rx_csum_fault() has been complaining that HW is providing bad checksums. Turns out the problem is in pskb_trim_rcsum_slow(), introduced in commit 88078d98d1bb ("net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends").
The source of the problem is that when the bytes we are trimming start at an odd address, as in the case of the 1 padding byte above, skb_checksum() returns a byte-swapped value. We cannot just combine this with skb->csum using csum_sub(). We need to use csum_block_sub() here that takes into account the parity of the start address and handles the swapping.
Matches existing code in __skb_postpull_rcsum() and esp_remove_trailer().
Fixes: 88078d98d1bb ("net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends") Signed-off-by: Dimitris Michailidis <dmichail@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Sasha Levin <sashal@kernel.org> --- net/core/skbuff.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 038ec74fa131..68ecb7d71c2b 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1585,8 +1585,9 @@ int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len) if (skb->ip_summed == CHECKSUM_COMPLETE) { int delta = skb->len - len; - skb->csum = csum_sub(skb->csum, - skb_checksum(skb, len, delta, 0)); + skb->csum = csum_block_sub(skb->csum, + skb_checksum(skb, len, delta, 0), + len); } return __pskb_trim(skb, len); } -- 2.17.1
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