Linux 4.16 cap_sys_module

[Stephen Smalley]

On 02/28/2018 08:53 AM, Stephen Smalley wrote:
> On 02/28/2018 04:53 AM, Dominick Grift wrote:
>> On Wed, Feb 28, 2018 at 10:27:08AM +0100, Dominick Grift wrote:
>>> Since Linux 4.16 (to atleast RC2) user space started to excessively trigger cap_sys_module
>>>
>>> Here is one example of such and event:
>>>
>>> type=SYSCALL msg=audit(02/27/2018 08:06:40.017:74) : arch=x86_64 syscall=ioctl success=no exit=ENOTTY(Inappropriate ioctl for device) a0=0x2 a1=TCGETS a2=0x7fff2d89f8f0 a3=0x55ba203a9010 items=0 ppid=1 pid=423 auid=unset uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=(none) ses=unset comm=systemd-user-se exe=/usr/lib/systemd/systemd-user-sessions subj=sys.id:sys.role:user_sessions.subj:s0 key=(null)
>>> type=AVC msg=audit(02/27/2018 08:06:40.017:74) : avc:  denied  { sys_module } for  pid=423 comm=systemd-user-se capability=sys_module  scontext=sys.id:sys.role:user_sessions.subj:s0 tcontext=sys.id:sys.role:user_sessions.subj:s0 tclass=capability permissive=1
>>> type=AVC msg=audit(02/27/2018 08:06:40.017:74) : avc:  denied  { module_request } for  pid=423 comm=systemd-user-se kmod=6E65746465762D80E72A05257F scontext=sys.id:sys.role:user_sessions.subj:s0 tcontext=sys.id:sys.role:sys.isid:s0 tclass=system permissive=1
>>>
>>> Any idea what causes this and how to fix it?
>>
>> For reference: https://github.com/fedora-selinux/selinux-policy/commit/2c13be1fb543c51935785e7a43b798a9f35f5aa0#comments
> 
> Looks like this might be caused by:
> 
> commit 44c02a2c3dc55835e9f0d8ef73966406cd805001
> Author: Al Viro <viro at zeniv.linux.org.uk>
> Date:   Thu Oct 5 12:59:44 2017 -0400
> 
>     dev_ioctl(): move copyin/copyout to callers
> 
>     Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
> 
> 
> It moves the dev_load() call out of the switch statement, which was only
> conditionally called in the default case if the cmd had certain values,
> and unconditionally calls it.  So we trigger module load denials on
> simple TCGETS (isatty) probes on a socket.  We need it moved back.

(expanded cc list since this affects more than just SELinux)

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