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Message-ID: <1460390286.3268.36.camel@redhat.com>
Date: Mon, 11 Apr 2016 10:58:06 -0500
From: Eric Paris <eparis@...hat.com>
To: Paul Moore <paul@...l-moore.com>, Andi Kleen <andi@...stfloor.org>
Cc: linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
linux-audit@...hat.com
Subject: Re: [PATCH] audit: Don't spam logs with SECCOMP_KILL/RET_ERRNO by
default
Just an FYI originally the idea was to follow the pattern of logging
set by core dumps see kernel/auditsc.c::audit_core_dumps(). Which is
gated by audit_enable but not anything else. I believe at that time the
only option was kill, which meant, much like the core dumper, spam was
not a likely result given the initiator is killed.
I'm all for a way to shut up unsolicited audit messages, especially
seccomp with errno or trap. I think it would be best to default 'KILL'
to on and everything else to off. I'm no so sure a sysctl is the right
way though. Enabling more forms of 'seccomp audit' should really be a
part of the audit policy.
(p.s. I think the action should be part of the seccomp message, as
right now all we know is that Andi's message isn't KILL since the
sig=0)
-Eric
On Mon, 2016-04-11 at 09:30 -0400, Paul Moore wrote:
> On Mon, Apr 11, 2016 at 12:13 AM, Andi Kleen <andi@...stfloor.org>
> wrote:
> >
> > From: Andi Kleen <ak@...ux.intel.com>
> >
> > When I run chrome on my opensuse system every time I open
> > a new tab the system log is spammed with:
> >
> > audit[16857]: SECCOMP auid=1000 uid=1000 gid=100 ses=1 pid=16857
> > comm="chrome" exe="/opt/google/chrome/chrome" sig=0 arch=c000003e
> > syscall=273 compat=0 ip=0x7fe27c11a444 code=0x50000
> >
> > This happens because chrome uses SECCOMP for its sandbox,
> > and for some reason always reaches a SECCOMP_KILL or more likely
> > SECCOMP_RET_ERRNO in the rule set.
> >
> > The seccomp auditing was originally added by Eric with
> >
> > commit 85e7bac33b8d5edafc4e219c7dfdb3d48e0b4e31
> > Author: Eric Paris <eparis@...hat.com>
> > Date: Tue Jan 3 14:23:05 2012 -0500
> >
> > seccomp: audit abnormal end to a process due to seccomp
> >
> > The audit system likes to collect information about
> > processes that end
> > abnormally (SIGSEGV) as this may me useful intrusion
> > detection information.
> > This patch adds audit support to collect information when
> > seccomp
> > forces a task to exit because of misbehavior in a similar
> > way.
> >
> > I don't have any other syscall auditing enabled,
> > just the standard user space auditing used by the systemd
> > and PAM userland. So basic auditing is alwas enabled,
> > but no other kernel auditing.
> >
> > Add a sysctl to enable this unconditional behavior with default
> > to off. This replaces an earlier patch that simply checked
> > whether syscall auditing was on, but Paul Moore preferred
> > this more elaborate approach.
> >
> > Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> > ---
> > Documentation/sysctl/kernel.txt | 9 +++++++++
> > include/linux/audit.h | 4 +++-
> > kernel/seccomp.c | 4 ++++
> > kernel/sysctl.c | 11 +++++++++++
> > 4 files changed, 27 insertions(+), 1 deletion(-)
> Quick response as I'm traveling the next few days and
> time/connectivity will be spotty ... thanks for sending an updated
> patch, some initial thoughts:
>
> * My thinking was that the sysctl knob could be a threshold value
> such
> that setting it to 0x00030000 would only log TRAP and KILL.
> * With the sysctl tunable defaulting to no-logging there is no need
> to
> check for audit_enabled, further, checking for audit_enabled would
> prevent logging to dmesg/syslog which I believe is valuable (you may
> not).
> * A bit nitpicky, but considering the possibility of logging to
> dmesg/syslog when auditing is disabled, I think
> "seccomp-log-threshold" or similar would be a better sysctl name.
>
> >
> > diff --git a/Documentation/sysctl/kernel.txt
> > b/Documentation/sysctl/kernel.txt
> > index 57653a4..abc6ef9 100644
> > --- a/Documentation/sysctl/kernel.txt
> > +++ b/Documentation/sysctl/kernel.txt
> > @@ -21,6 +21,7 @@ show up in /proc/sys/kernel:
> > - acct
> > - acpi_video_flags
> > - auto_msgmni
> > +- audit_log_seccomp
> > - bootloader_type [ X86 only ]
> > - bootloader_version [ X86 only ]
> > - callhome [ S390 only ]
> > @@ -129,6 +130,14 @@ upon memory add/remove or upon ipc namespace
> > creation/removal.
> > Echoing "1" into this file enabled msgmni automatic recomputing.
> > Echoing "0" turned it off. auto_msgmni default value was 1.
> >
> > +==============================================================
> > +
> > +audit_log_seccomp
> > +
> > +When this variable is set to 1 every
> > SECCOMP_KILL/SECCOMP_RET_ERRNO
> > +results in an audit log. This is generally a bad idea because
> > +it leads to a audit message every time Chrome opens a new tab.
> > +Defaults to 0.
> >
> > ==============================================================
> >
> > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > index e38e3fc..c7787ba 100644
> > --- a/include/linux/audit.h
> > +++ b/include/linux/audit.h
> > @@ -315,9 +315,11 @@ static inline void audit_inode_child(struct
> > inode *parent,
> > }
> > void audit_core_dumps(long signr);
> >
> > +extern int audit_log_seccomp;
> > +
> > static inline void audit_seccomp(unsigned long syscall, long
> > signr, int code)
> > {
> > - if (!audit_enabled)
> > + if (!audit_enabled || !audit_log_seccomp)
> > return;
> >
> > /* Force a record to be reported if a signal was delivered.
> > */
> > diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> > index e1e5a35..09a8b03 100644
> > --- a/kernel/seccomp.c
> > +++ b/kernel/seccomp.c
> > @@ -25,6 +25,10 @@
> > #include <asm/syscall.h>
> > #endif
> >
> > +#ifdef CONFIG_AUDIT
> > +int audit_log_seccomp __read_mostly = 0;
> > +#endif
> > +
> > #ifdef CONFIG_SECCOMP_FILTER
> > #include <linux/filter.h>
> > #include <linux/pid.h>
> > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > index 725587f..0c7611e 100644
> > --- a/kernel/sysctl.c
> > +++ b/kernel/sysctl.c
> > @@ -65,6 +65,7 @@
> > #include <linux/sched/sysctl.h>
> > #include <linux/kexec.h>
> > #include <linux/bpf.h>
> > +#include <linux/audit.h>
> >
> > #include <asm/uaccess.h>
> > #include <asm/processor.h>
> > @@ -529,6 +530,16 @@ static struct ctl_table kern_table[] = {
> > .proc_handler = proc_dointvec,
> > },
> > #endif
> > +#ifdef CONFIG_AUDIT
> > + {
> > + .procname = "audit-log-seccomp",
> > + .data = &audit_log_seccomp,
> > + .maxlen = sizeof(int),
> > + .mode = 0644,
> > + .proc_handler = proc_dointvec,
> > + },
> > +
> > +#endif
> > {
> > .procname = "print-fatal-signals",
> > .data = &print_fatal_signals,
> > --
> > 2.7.4
> >
>
>
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