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net-timestamp: no-payload only sysctl

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Tx timestamps are looped onto the error queue on top of an skb. This
mechanism leaks packet headers to processes unless the no-payload
options SOF_TIMESTAMPING_OPT_TSONLY is set.

Add a sysctl that optionally drops looped timestamp with data. This
only affects processes without CAP_NET_RAW.

The policy is checked when timestamps are generated in the stack.
It is possible for timestamps with data to be reported after the
sysctl is set, if these were queued internally earlier.

No vulnerability is immediately known that exploits knowledge
gleaned from packet headers, but it may still be preferable to allow
administrators to lock down this path at the cost of possible
breakage of legacy applications.

Signed-off-by: Willem de Bruijn <willemb@google.com>

----

Changes
  (v1 -> v2)
  - test socket CAP_NET_RAW instead of capable(CAP_NET_RAW)
  (rfc -> v1)
  - document the sysctl in Documentation/sysctl/net.txt
  - fix access control race: read .._OPT_TSONLY only once,
        use same value for permission check and skb generation.
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Willem de Bruijn
2015-01-30 13:29:32 -05:00
committed by David S. Miller
parent 49ca0d8bfa
commit b245be1f4d
5 changed files with 41 additions and 1 deletions
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8
Documentation/sysctl/net.txt
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@@ -97,6 +97,14 @@ rmem_max
The maximum receive socket buffer size in bytes.
tstamp_allow_data
-----------------
Allow processes to receive tx timestamps looped together with the original
packet contents. If disabled, transmit timestamp requests from unprivileged
processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set.
Default: 1 (on)
wmem_default
------------