Synopsis: Important: kernel security and bug fix update
Advisory ID: SLSA-2018:0169-1
Issue Date: 2018-01-25
CVE Numbers: CVE-2017-9074
* An integer overflow vulnerability in ip6_find_1stfragopt() function was
found. A local attacker that has privileges (of CAP_NET_RAW) to open raw
socket can cause an infinite loop inside the ip6_find_1stfragopt()
function. (CVE-2017-7542, Moderate)
* The IPv6 fragmentation implementation in the Linux kernel does not
consider that the nexthdr field may be associated with an invalid option,
which allows local users to cause a denial of service (out-of-bounds read
and BUG) or possibly have unspecified other impact via crafted socket and
send system calls. Due to the nature of the flaw, privilege escalation
cannot be fully ruled out, although we believe it is unlikely.
* A use-after-free flaw was found in the Netlink functionality of the
Linux kernel networking subsystem. Due to the insufficient cleanup in the
mq_notify function, a local attacker could potentially use this flaw to
escalate their privileges on the system. (CVE-2017-11176, Moderate)
* Previously, the default timeout and retry settings in the VMBus driver
were insufficient in some cases, for example when a Hyper-V host was under
a significant load. Consequently, in Windows Server 2016, Hyper-V Server
2016, and Windows Azure Platform, when running a Scientific Linux Guest on
the Hyper-V hypervisor, the guest failed to boot or booted with certain
Hyper-V devices missing. This update alters the timeout and retry settings
in VMBus, and Scientific Linux guests now boot as expected under the
* Previously, an incorrect external declaration in the be2iscsi driver
caused a kernel panic when using the systool utility. With this update,
the external declaration in be2iscsi has been fixed, and the kernel no
longer panics when using systool.
* Under high usage of the NFSD file system and memory pressure, if many
tasks in the Linux kernel attempted to obtain the global spinlock to clean
the Duplicate Reply Cache (DRC), these tasks stayed in an active wait in
the nfsd_reply_cache_shrink() function for up to 99% of time.
Consequently, a high load average occurred. This update fixes the bug by
separating the DRC in several parts, each with an independent spinlock. As
a result, the load and CPU utilization is no longer excessive under the
* When attempting to attach multiple SCSI devices simultaneously,
Scientific Linux 6.9 on IBM z Systems sometimes became unresponsive. This
update fixes the zfcp device driver, and attaching multiple SCSI devices
simultaneously now works as expected in the described scenario.
* On IBM z Systems, the tiqdio_call_inq_handlers() function in the Linux
kernel incorrectly cleared the device state change indicator (DSCI) for
the af_iucv devices using the HiperSockets transport with multiple input
queues. Consequently, queue stalls on such devices occasionally occurred.
With this update, tiqdio_call_inq_handlers() has been fixed to clear the
DSCI only once, prior to scanning the queues. As a result, queue stalls
for af_iucv devices using the HiperSockets transport no longer occur under
the described circumstances.
* Previously, small data chunks caused the Stream Control Transmission
Protocol (SCTP) to account the receiver_window (rwnd) values incorrectly
when recovering from a “zero-window situation”. As a consequence, window
updates were not sent to the peer, and an artificial growth of rwnd could
lead to packet drops. This update properly accounts such small data chunks
and ignores the rwnd pressure values when reopening a window. As a result,
window updates are now sent, and the announced rwnd reflects better the
real state of the receive buffer.
– Scientific Linux Development Team