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DescriptionNikolai Kondrashov
2017-02-24 14:14:45 UTC
Description of problem:
When FreeRADIUS starts, it calls ptrace on itself to determine if it's running under a debugger. That is later used to decide whether to break into the debugger, or simply exit, when a critical error occurs.
However, SELinux policy prevents it from executing ptrace:
type=AVC msg=audit(1487944609.686:744): avc: denied { ptrace } for pid=15592 comm="radiusd" scontext=system_u:system_r:radiusd_t:s0 tcontext=system_u:system_r:radiusd_t:s0 tclass=process
type=SYSCALL msg=audit(1487944609.686:744): arch=c000003e syscall=101 success=no exit=-13 a0=10 a1=3ce6 a2=0 a3=0 items=0 ppid=15590 pid=15592 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="radiusd" exe="/usr/sbin/radiusd" subj=system_u:system_r:radiusd_t:s0 key
=(null)
Since ptrace reports the same error code for both permission denied and already being traced, FreeRADIUS assumes it is already running under a debugger. That results in FreeRADIUS killing itself with SIGTRAP, when it attempts to break into the non-existent debugger, upon a critical error.
Since FreeRADIUS drops into a dedicated uid/gid after startup, there doesn't seem to be much danger of letting it use the ptrace call.
Please consider changing the policy to let FreeRADIUS execute ptrace, perhaps only when running as root.
Version-Release number of selected component (if applicable):
selinux-policy-3.13.1-102.el7_3.13.noarch
freeradius-3.0.12-2.el7.x86_64
How reproducible:
Always
Steps to Reproduce:
sudo service radiusd start
sudo grep 'denied.*ptrace.*radiusd' /var/log/audit/audit.log | tail -n1
Actual results:
type=AVC msg=audit(1487944609.686:744): avc: denied { ptrace } for pid=15592 comm="radiusd" scontext=system_u:system_r:radiusd_t:s0 tcontext=system_u:system_r:radiusd_t:s0 tclass=process
Expected results:
No output
Additional info:
Code calling ptrace in FreeRADIUS:
https://github.com/FreeRADIUS/freeradius-server/blob/release_3_0_12/src/lib/debug.c#L120
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-2017:1861
Description of problem: When FreeRADIUS starts, it calls ptrace on itself to determine if it's running under a debugger. That is later used to decide whether to break into the debugger, or simply exit, when a critical error occurs. However, SELinux policy prevents it from executing ptrace: type=AVC msg=audit(1487944609.686:744): avc: denied { ptrace } for pid=15592 comm="radiusd" scontext=system_u:system_r:radiusd_t:s0 tcontext=system_u:system_r:radiusd_t:s0 tclass=process type=SYSCALL msg=audit(1487944609.686:744): arch=c000003e syscall=101 success=no exit=-13 a0=10 a1=3ce6 a2=0 a3=0 items=0 ppid=15590 pid=15592 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="radiusd" exe="/usr/sbin/radiusd" subj=system_u:system_r:radiusd_t:s0 key =(null) Since ptrace reports the same error code for both permission denied and already being traced, FreeRADIUS assumes it is already running under a debugger. That results in FreeRADIUS killing itself with SIGTRAP, when it attempts to break into the non-existent debugger, upon a critical error. Since FreeRADIUS drops into a dedicated uid/gid after startup, there doesn't seem to be much danger of letting it use the ptrace call. Please consider changing the policy to let FreeRADIUS execute ptrace, perhaps only when running as root. Version-Release number of selected component (if applicable): selinux-policy-3.13.1-102.el7_3.13.noarch freeradius-3.0.12-2.el7.x86_64 How reproducible: Always Steps to Reproduce: sudo service radiusd start sudo grep 'denied.*ptrace.*radiusd' /var/log/audit/audit.log | tail -n1 Actual results: type=AVC msg=audit(1487944609.686:744): avc: denied { ptrace } for pid=15592 comm="radiusd" scontext=system_u:system_r:radiusd_t:s0 tcontext=system_u:system_r:radiusd_t:s0 tclass=process Expected results: No output Additional info: Code calling ptrace in FreeRADIUS: https://github.com/FreeRADIUS/freeradius-server/blob/release_3_0_12/src/lib/debug.c#L120