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DescriptionMiroslav Lichvar
2018-05-16 14:33:03 UTC
Description of problem:
When using the timemaster service from the linuxptp package, a shared memory segment is used to exchange measurements between chronyd and ptp4l or phc2sys. The memory segment can be created by any of the three processes. There is a race. Usually it's chronyd what creates the memory segment and that's when it works, but if it's phc2sys or ptp4l, chronyd is not able to get the segment due to a SELinux rule.
type=AVC msg=audit(1525261575.377:77): avc: denied { unix_read unix_write } for pid=1342 comm="chronyd" key=1314148400 scontext=system_u:system_r:chronyd_t:s0 tcontext=system_u:system_r:phc2sys_t:s0 tclass=shm
A similar issue is with segments created by ptp4l (using SW timestamping) when switching to phc2sys (using HW timestamping).
type=AVC msg=audit(1525263148.431:75): avc: denied { unix_read unix_write } for pid=1366 comm="phc2sys" key=1314148401 scontext=system_u:system_r:phc2sys_t:s0 tcontext=system_u:system_r:ptp4l_t:s0 tclass=shm
Version-Release number of selected component (if applicable):
selinux-policy-3.13.1-192.el7_5.3.noarch
How reproducible:
sometimes
Steps to Reproduce:
1. remove existing segments (e.g. with ipcrm -M 0x4e545030)
1. start timemaster configured to use at least one PTP source, e.g.
[ptp_domain 0]
interfaces eth0
2. check the system log
Actual results:
chronyd[840]: Fatal error : shmget() failed
Expected results:
chronyd running with no AVCs reported in the logs.
Additional info:
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2018:3111
Description of problem: When using the timemaster service from the linuxptp package, a shared memory segment is used to exchange measurements between chronyd and ptp4l or phc2sys. The memory segment can be created by any of the three processes. There is a race. Usually it's chronyd what creates the memory segment and that's when it works, but if it's phc2sys or ptp4l, chronyd is not able to get the segment due to a SELinux rule. type=AVC msg=audit(1525261575.377:77): avc: denied { unix_read unix_write } for pid=1342 comm="chronyd" key=1314148400 scontext=system_u:system_r:chronyd_t:s0 tcontext=system_u:system_r:phc2sys_t:s0 tclass=shm A similar issue is with segments created by ptp4l (using SW timestamping) when switching to phc2sys (using HW timestamping). type=AVC msg=audit(1525263148.431:75): avc: denied { unix_read unix_write } for pid=1366 comm="phc2sys" key=1314148401 scontext=system_u:system_r:phc2sys_t:s0 tcontext=system_u:system_r:ptp4l_t:s0 tclass=shm Version-Release number of selected component (if applicable): selinux-policy-3.13.1-192.el7_5.3.noarch How reproducible: sometimes Steps to Reproduce: 1. remove existing segments (e.g. with ipcrm -M 0x4e545030) 1. start timemaster configured to use at least one PTP source, e.g. [ptp_domain 0] interfaces eth0 2. check the system log Actual results: chronyd[840]: Fatal error : shmget() failed Expected results: chronyd running with no AVCs reported in the logs. Additional info: