Add Linux 4.19.52 #1137
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Add Linux 4.19.52 #1137
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This fixes *Linux and FreeBSD Kernel: Multiple TCP-based remote denial of service issues* [1]. > Netflix has identified several TCP networking vulnerabilities in FreeBSD > and Linux kernels. > > The vulnerabilities specifically relate to the minimum segment size (MSS) > and TCP Selective Acknowledgement (SACK) capabilities. The most serious, > dubbed “SACK Panic,” allows a remotely-triggered kernel panic on recent > Linux kernels. > > There are patches that address most of these vulnerabilities. If patches > can not be applied, certain mitigations will be effective. We recommend > that affected parties enact one of those described below, based on their > environment. > > #1: CVE-2019-11477: SACK Panic (Linux >= 2.6.29) > > Description: A sequence of SACKs may be crafted such that one can trigger > an integer overflow, leading to a kernel panic. > > Fix: Apply the attached patch (“PATCH_net_1_4.patch”). Additionally, > versions of the Linux kernel up to, and including, 4.14 require a second > patch (“PATCH_net_1a.patch”). > > Workaround #1: Block connections with a low MSS using one of the attached > filters. (The values in the filters are examples. You can apply a higher or > lower limit, as appropriate for your environment.) Note that these filters > may break legitimate connections which rely on a low MSS. Also, note that > this mitigation is only effective if TCP probing is disabled (that is, the > net.ipv4.tcp_mtu_probing sysctl is set to 0, which appears to be the > default value for that sysctl). > > Workaround #2: Disable SACK processing (/proc/sys/net/ipv4/tcp_sack set to > 0). > > (Note that either workaround should be sufficient on its own. It is not > necessary to apply both workarounds.) > > > #2: CVE-2019-11478: SACK Slowness (Linux < 4.15) or Excess Resource Usage > (all Linux versions) > > Description: It is possible to send a crafted sequence of SACKs which will > fragment the TCP retransmission queue. On Linux kernels prior to 4.15, an > attacker may be able to further exploit the fragmented queue to cause an > expensive linked-list walk for subsequent SACKs received for that same TCP > connection. > > Fix: Apply the attached patch (“PATCH_net_2_4.patch”) > > Workaround #1: Block connections with a low MSS using one of the attached > filters. (The values in the filters are examples. You can apply a higher or > lower limit, as appropriate for your environment.) Note that these filters > may break legitimate connections which rely on a low MSS. Also, note that > this mitigation is only effective if TCP probing is disabled (that is, the > net.ipv4.tcp_mtu_probing sysctl is set to 0, which appears to be the > default value for that sysctl). > > Workaround #2: Disable SACK processing (/proc/sys/net/ipv4/tcp_sack set to > 0). > > (Note that either workaround should be sufficient on its own. It is not > necessary to apply both workarounds.) > > > #3: CVE-2019-5599: SACK Slowness (FreeBSD 12 using the RACK TCP Stack) > > Description: It is possible to send a crafted sequence of SACKs which will > fragment the RACK send map. An attacker may be able to further exploit the > fragmented send map to cause an expensive linked-list walk for subsequent > SACKs received for that same TCP connection. > > Workaround #1: Apply the attached patch (“split_limit.patch”) and set the > net.inet.tcp.rack.split_limit sysctl to a reasonable value to limit the > size of the SACK table. > > Workaround #2: Temporarily disable the RACK TCP stack. > > (Note that either workaround should be sufficient on its own. It is not > necessary to apply both workarounds.) > > > #4: CVE-2019-11479: Excess Resource Consumption Due to Low MSS Values (all > Linux versions) > > Description: An attacker can force the Linux kernel to segment its > responses into multiple TCP segments, each of which contains only 8 bytes > of data. This drastically increases the bandwidth required to deliver the > same amount of data. Further, it consumes additional resources (CPU and NIC > processing power). This attack requires continued effort from the attacker > and the impacts will end shortly after the attacker stops sending traffic. > > Fix: Two attached patches (“PATCH_net_3_4.patch” and “PATCH_net_4_4.patch”) > add a sysctl which enforces a minimum MSS, set by the > net.ipv4.tcp_min_snd_mss sysctl. This lets an administrator enforce a > minimum MSS appropriate for their applications. > > Workaround: Block connections with a low MSS using one of the attached > filters. (The values in the filters are examples. You can apply a higher or > lower limit, as appropriate for your environment.) Note that these filters > may break legitimate connections which rely on a low MSS. Also, note that > this mitigation is only effective if TCP probing is disabled (that is, the > net.ipv4.tcp_mtu_probing sysctl is set to 0, which appears to be the > default value for that sysctl). > > > Note: Good system and application coding and configuration practices > (limiting write buffers to the necessary level, monitoring connection > memory consumption via SO_MEMINFO, and aggressively closing misbehaving > connections) can help to limit the impact of attacks against these kinds of > vulnerabilities. > > An advisory has been published > at https://github.com/Netflix/security-bulletins/blob/master/advisories/third-party/2019-001.md > > Acknowledgments: > Originally reported by Jonathan Looney. > We thank Eric Dumazet for providing Linux fixes and support. > We thank Bruce Curtis for providing the Linux filters. > We thank Jonathan Lemon and Alexey Kodanev for helping to improve the Linux > patches. > We gratefully acknowledge the assistance of Tyler Hicks in testing fixes, > refining the information about vulnerable versions, and providing > assistance during the disclosure process. > > Regards, > Netflix Information Security The other commits between 4.19.40 and 4.19.52 can be found in the [git repository][2]. [1]: https://www.openwall.com/lists/oss-security/2019/06/17/5 [2]: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/log/?h=linux-4.19.y
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Tested on stitch, inbetweenmove (AMDGPU), and sigusr2 (Nouveau).