[PATCH 1/1] audit: Record fanotify access control decisions
Richard Guy Briggs
rgb at redhat.com
Wed Sep 6 15:57:16 UTC 2017
On 2017-09-06 10:20, Steve Grubb wrote:
> On Tuesday, September 5, 2017 11:24:49 PM EDT Richard Guy Briggs wrote:
> > On 2017-09-05 14:32, Steve Grubb wrote:
> > > The fanotify interface allows user space daemons to make access
> > >
> > > control decisions. Under common criteria requirements, we need to
> > > optionally record decisions based on policy. This patch adds a bit mask,
> > > FAN_AUDIT, that a user space daemon can 'or' into the response decision
> > > which will tell the kernel that it made a decision and record it.
> > >
> > > It would be used something like this in user space code:
> > > response.response = FAN_DENY | FAN_AUDIT;
> > > write(fd, &response, sizeof(struct fanotify_response));
> > >
> > > When the syscall ends, the audit system will record the decision as a
> > > AUDIT_FANOTIFY auxiliary record to denote that the reason this event
> > > occurred is the result of an access control decision from fanotify
> > > rather than DAC or MAC policy.
> > >
> > > A sample event looks like this:
> > >
> > > type=PATH msg=audit(1504310584.332:290): item=0 name="./evil-ls"
> > > inode=1319561 dev=fc:03 mode=0100755 ouid=1000 ogid=1000 rdev=00:00
> > > obj=unconfined_u:object_r:user_home_t:s0 nametype=NORMAL
> > > type=CWD msg=audit(1504310584.332:290): cwd="/home/sgrubb"
> > > type=SYSCALL msg=audit(1504310584.332:290): arch=c000003e syscall=2
> > > success=no exit=-1 a0=32cb3fca90 a1=0 a2=43 a3=8 items=1 ppid=901
> > > pid=959 auid=1000 uid=1000 gid=1000 euid=1000 suid=1000
> > > fsuid=1000 egid=1000 sgid=1000 fsgid=1000 tty=pts1 ses=3 comm="bash"
> > > exe="/usr/bin/bash" subj=unconfined_u:unconfined_r:unconfined_t:
> > > s0-s0:c0.c1023 key=(null)
> > > type=FANOTIFY msg=audit(1504310584.332:290): resp=2
> > >
> > > Signed-off-by: sgrubb <sgrubb at redhat.com>
> >
> > In the AUDIT_FANOTIFY record, there is a new field "resp". Should this
> > not conform to the existing field types "res" or "result"?
>
> The values used by fanotify are either 1 & 2 rather than 0 & 1. So, it would
> need record specific translation. It's easier to just pick a new field name
> and key off of that.
Ah, fair enough. That's unfortunate.
> -Steve
>
> > Other than that,
> > Reviewed-by: Richard Guy Briggs <rgb at redhat.com>
> >
> > > ---
> > >
> > > fs/notify/fanotify/fanotify.c | 8 +++++++-
> > > fs/notify/fanotify/fanotify_user.c | 2 +-
> > > include/linux/audit.h | 7 +++++++
> > > include/uapi/linux/audit.h | 1 +
> > > include/uapi/linux/fanotify.h | 2 ++
> > > kernel/auditsc.c | 6 ++++++
> > > 6 files changed, 24 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> > > index 2fa99ae..1968d21 100644
> > > --- a/fs/notify/fanotify/fanotify.c
> > > +++ b/fs/notify/fanotify/fanotify.c
> > > @@ -9,6 +9,7 @@
> > >
> > > #include <linux/sched/user.h>
> > > #include <linux/types.h>
> > > #include <linux/wait.h>
> > >
> > > +#include <linux/audit.h>
> > >
> > > #include "fanotify.h"
> > >
> > > @@ -78,7 +79,7 @@ static int fanotify_get_response(struct fsnotify_group
> > > *group,>
> > > fsnotify_finish_user_wait(iter_info);
> > >
> > > out:
> > > /* userspace responded, convert to something usable */
> > >
> > > - switch (event->response) {
> > > + switch (event->response & ~FAN_AUDIT) {
> > >
> > > case FAN_ALLOW:
> > > ret = 0;
> > > break;
> > >
> > > @@ -86,6 +87,11 @@ static int fanotify_get_response(struct fsnotify_group
> > > *group,>
> > > default:
> > > ret = -EPERM;
> > >
> > > }
> > >
> > > +
> > > + /* Check if the response should be audited */
> > > + if (event->response & FAN_AUDIT)
> > > + audit_fanotify(event->response & ~FAN_AUDIT);
> > > +
> > >
> > > event->response = 0;
> > >
> > > pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
> > >
> > > diff --git a/fs/notify/fanotify/fanotify_user.c
> > > b/fs/notify/fanotify/fanotify_user.c index 907a481..b983b5c 100644
> > > --- a/fs/notify/fanotify/fanotify_user.c
> > > +++ b/fs/notify/fanotify/fanotify_user.c
> > > @@ -179,7 +179,7 @@ static int process_access_response(struct
> > > fsnotify_group *group,>
> > > * userspace can send a valid response or we will clean it up after the
> > > * timeout
> > > */
> > >
> > > - switch (response) {
> > > + switch (response & ~FAN_AUDIT) {
> > >
> > > case FAN_ALLOW:
> > >
> > > case FAN_DENY:
> > > break;
> > >
> > > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > > index 2150bdc..bf55732 100644
> > > --- a/include/linux/audit.h
> > > +++ b/include/linux/audit.h
> > > @@ -360,6 +360,7 @@ extern int __audit_log_bprm_fcaps(struct linux_binprm
> > > *bprm,>
> > > extern void __audit_log_capset(const struct cred *new, const struct cred
> > > *old); extern void __audit_mmap_fd(int fd, int flags);
> > > extern void __audit_log_kern_module(char *name);
> > >
> > > +extern void __audit_fanotify(unsigned int response);
> > >
> > > static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp)
> > > {
> > >
> > > @@ -456,6 +457,12 @@ static inline void audit_log_kern_module(char *name)
> > >
> > > __audit_log_kern_module(name);
> > >
> > > }
> > >
> > > +static inline void audit_fanotify(unsigned int response)
> > > +{
> > > + if (!audit_dummy_context())
> > > + __audit_fanotify(response);
> > > +}
> > > +
> > >
> > > extern int audit_n_rules;
> > > extern int audit_signals;
> > > #else /* CONFIG_AUDITSYSCALL */
> > >
> > > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > > index 0714a66..221f8b7 100644
> > > --- a/include/uapi/linux/audit.h
> > > +++ b/include/uapi/linux/audit.h
> > > @@ -112,6 +112,7 @@
> > >
> > > #define AUDIT_FEATURE_CHANGE 1328 /* audit log listing feature changes */
> > > #define AUDIT_REPLACE 1329 /* Replace auditd if this packet
> unanswerd */
> > > #define AUDIT_KERN_MODULE 1330 /* Kernel Module events */
> > >
> > > +#define AUDIT_FANOTIFY 1331 /* Fanotify access decision */
> > >
> > > #define AUDIT_AVC 1400 /* SE Linux avc denial or grant */
> > > #define AUDIT_SELINUX_ERR 1401 /* Internal SE Linux Errors */
> > >
> > > diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
> > > index 030508d..5681e44 100644
> > > --- a/include/uapi/linux/fanotify.h
> > > +++ b/include/uapi/linux/fanotify.h
> > > @@ -99,6 +99,8 @@ struct fanotify_response {
> > >
> > > /* Legit userspace responses to a _PERM event */
> > > #define FAN_ALLOW 0x01
> > > #define FAN_DENY 0x02
> > >
> > > +#define FAN_AUDIT 0x80 /* Bit mask to create audit record for result */
> > > +
> > >
> > > /* No fd set in event */
> > > #define FAN_NOFD -1
> > >
> > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > > index 3260ba2..1725f73 100644
> > > --- a/kernel/auditsc.c
> > > +++ b/kernel/auditsc.c
> > > @@ -2390,6 +2390,12 @@ void __audit_log_kern_module(char *name)
> > >
> > > context->type = AUDIT_KERN_MODULE;
> > >
> > > }
> > >
> > > +void __audit_fanotify(unsigned int response)
> > > +{
> > > + audit_log(current->audit_context, GFP_ATOMIC,
> > > + AUDIT_FANOTIFY, "resp=%u", response);
> > > +}
> > > +
> > >
> > > static void audit_log_task(struct audit_buffer *ab)
> > > {
> > >
> > > kuid_t auid, uid;
> >
> > - RGB
> >
> > --
> > Richard Guy Briggs <rgb at redhat.com>
> > Sr. S/W Engineer, Kernel Security, Base Operating Systems
> > Remote, Ottawa, Red Hat Canada
> > IRC: rgb, SunRaycer
> > Voice: +1.647.777.2635, Internal: (81) 32635
>
>
- RGB
--
Richard Guy Briggs <rgb at redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635
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