[TCP]: Fix fastpath_cnt_hint when GSO skb is partially ACKed

When only GSO skb was partially ACKed, no hints are reset, therefore fastpath_cnt_hint must be tweaked too or else it can corrupt fackets_out. The corruption to occur, one must have non-trivial ACK/SACK sequence, so this bug is not very often that harmful. There's a fackets_out state reset in TCP because fackets_out is known to be inaccurate and that fixes the issue eventually anyway. In case there was also at least one skb that got fully ACKed, the fastpath_skb_hint is set to NULL which causes a recount for fastpath_cnt_hint (the old value won't be accessed anymore), thus it can safely be decremented without additional checking. Reported by Cedric Le Goater <clg@fr.ibm.com> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>

[TCP]: Fix fastpath_cnt_hint when GSO skb is partially ACKed
When only GSO skb was partially ACKed, no hints are reset, therefore fastpath_cnt_hint must be tweaked too or else it can corrupt fackets_out. The corruption to occur, one must have non-trivial ACK/SACK sequence, so this bug is not very often that harmful. There's a fackets_out state reset in TCP because fackets_out is known to be inaccurate and that fixes the issue eventually anyway. In case there was also at least one skb that got fully ACKed, the fastpath_skb_hint is set to NULL which causes a recount for fastpath_cnt_hint (the old value won't be accessed anymore), thus it can safely be decremented without additional checking. Reported by Cedric Le Goater <clg@fr.ibm.com> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
Ilpo Järvinen · David S. Miller
1 parent 3eb215de26
Showing 1 changed file with 3 additions and 0 deletions Side-by-side Diff
net/ipv4/tcp_input.c
@@ -2420,6 +2420,9 @@
 			__u32 dval = min(tp->fackets_out, packets_acked);
 			tp->fackets_out -= dval;
 		}
+		/* hint's skb might be NULL but we don't need to care */
+		tp->fastpath_cnt_hint -= min_t(u32, packets_acked,
+					       tp->fastpath_cnt_hint);
 		tp->packets_out -= packets_acked;
  
 		BUG_ON(tcp_skb_pcount(skb) == 0);
...	...	@@ -2420,6 +2420,9 @@
2420	2420	__u32 dval = min(tp->fackets_out, packets_acked);
2421	2421	tp->fackets_out -= dval;
2422	2422	}
	2423	+ /* hint's skb might be NULL but we don't need to care */
	2424	+ tp->fastpath_cnt_hint -= min_t(u32, packets_acked,
	2425	+ tp->fastpath_cnt_hint);
2423	2426	tp->packets_out -= packets_acked;
2424	2427
2425	2428	BUG_ON(tcp_skb_pcount(skb) == 0);