upstream: 5424ea27390f ("netns: get more entropy from net_hash_mix()")
struct net are effectively allocated from order-1 pages on x86,
with one object per slab, meaning that the 13 low order bits
of their addresses are zero.
Once shifted by L1_CACHE_SHIFT, this leaves 7 zero-bits,
meaning that net_hash_mix() does not help spreading
objects on various hash tables.
For example, TCP listen table has 32 buckets, meaning that
all netns use the same bucket for port 80 or port 443.
Signed-off-by: Hongbo Li <herberthbli@tencent.com>
[upstream commit 5f3e2bf008c2221478101ee72f5cb4654b9fc363]
Some TCP peers announce a very small MSS option in their SYN and/or
SYN/ACK messages.
This forces the stack to send packets with a very high network/cpu
overhead.
Linux has enforced a minimal value of 48. Since this value includes
the size of TCP options, and that the options can consume up to 40
bytes, this means that each segment can include only 8 bytes of payload.
In some cases, it can be useful to increase the minimal value
to a saner value.
We still let the default to 48 (TCP_MIN_SND_MSS), for compatibility
reasons.
Note that TCP_MAXSEG socket option enforces a minimal value
of (TCP_MIN_MSS). David Miller increased this minimal value
in commit c39508d6f118 ("tcp: Make TCP_MAXSEG minimum more correct.")
from 64 to 88.
We might in the future merge TCP_MIN_SND_MSS and TCP_MIN_MSS.
CVE-2019-11479 -- tcp mss hardcoded to 48
[upstream commit: 967c05aee439e6e5d7d805e195b3a20ef5c433d6]
tcp: enforce tcp_min_snd_mss in tcp_mtu_probing()
If mtu probing is enabled tcp_mtu_probing() could very well end up
with a too small MSS.
Use the new sysctl tcp_min_snd_mss to make sure MSS search
is performed in an acceptable range.
Signed-off-by: Zhiping Du <zhipingdu@tencent.com>
upstream commit: 356d1833b638bd465672aefeb71def3ab93fc17d
Note that when a new netns is created, it inherits its
sysctl_tcp_rmem and sysctl_tcp_wmem from initial netns.
This change is needed so that we can refine TCP rcvbuf autotuning,
to take RTT into consideration.
Signed-off-by: Hongbo Li <herberthbli@tencent.com>
Hongbo Li