Re: [PATCH 1/1] audit: Record fanotify access control decisions

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On Tue, Sep 5, 2017 at 2:32 PM, Steve Grubb <sgrubb@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
>  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(-)

The audit bits look fine to me, although considering the timing, this
really shouldn't be merged anywhere until after the current merge
window closes.

Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>

> 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;
> --
> 2.9.5
>
>
> --
> Linux-audit mailing list
> Linux-audit@xxxxxxxxxx
> https://www.redhat.com/mailman/listinfo/linux-audit



-- 
paul moore
www.paul-moore.com



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