[PATCH v5 3/3] fanotify, audit: Allow audit to use the full permission event response

[Steve Grubb]

Hello,

Sorry to take so long. Holidays and kernel build problems. However, I have 
built a kernel with these patches. I only have 2 comments. When I use an 
application that expected the old API, meaning it simply does:

        response.fd = metadata->fd;
        response.response = reply;
        close(metadata->fd);
        write(fd, &response, sizeof(struct fanotify_response));

I get access denials. Every time. If the program is using the new API and 
sets FAN_INFO, then it works as expected. I'll do some more testing but I 
think there is something wrong in the compatibility path.

On Monday, December 12, 2022 9:06:11 AM EST Richard Guy Briggs wrote:
> This patch passes the full response so that the audit function can use all
> of it. The audit function was updated to log the additional information in
> the AUDIT_FANOTIFY record.

What I'm seeing is:

type=FANOTIFY msg=audit(01/09/2023 18:43:16.306:366) : resp=deny fan_type=1 
fan_info=313300000000000000000000 subj_trust=0 obj_trust=0

Where fan_info was supposed to be 13 decimal. More below...

> Currently the only type of fanotify info that is defined is an audit
> rule number, but convert it to hex encoding to future-proof the field.
> Hex encoding suggested by Paul Moore <paul at paul-moore.com>.
> 
> Sample records:
>   type=FANOTIFY msg=audit(1600385147.372:590): resp=2 fan_type=1
> fan_info=3137 subj_trust=3 obj_trust=5 type=FANOTIFY
> msg=audit(1659730979.839:284): resp=1 fan_type=0 fan_info=3F subj_trust=2
> obj_trust=2
> 
> Suggested-by: Steve Grubb <sgrubb at redhat.com>
> Link: https://lore.kernel.org/r/3075502.aeNJFYEL58@x2
> Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
> ---
>  fs/notify/fanotify/fanotify.c |  3 ++-
>  include/linux/audit.h         |  9 +++++----
>  kernel/auditsc.c              | 25 ++++++++++++++++++++++---
>  3 files changed, 29 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index 24ec1d66d5a8..29bdd99b29fa 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -273,7 +273,8 @@ static int fanotify_get_response(struct fsnotify_group
> *group,
> 
>  	/* Check if the response should be audited */
>  	if (event->response & FAN_AUDIT)
> -		audit_fanotify(event->response & ~FAN_AUDIT);
> +		audit_fanotify(event->response & ~FAN_AUDIT,
> +			       &event->audit_rule);
> 
>  	pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
>  		 group, event, ret);
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index d6b7d0c7ce43..31086a72e32a 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -14,6 +14,7 @@
>  #include <linux/audit_arch.h>
>  #include <uapi/linux/audit.h>
>  #include <uapi/linux/netfilter/nf_tables.h>
> +#include <uapi/linux/fanotify.h>
> 
>  #define AUDIT_INO_UNSET ((unsigned long)-1)
>  #define AUDIT_DEV_UNSET ((dev_t)-1)
> @@ -416,7 +417,7 @@ 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_openat2_how(struct open_how *how);
>  extern void __audit_log_kern_module(char *name);
> -extern void __audit_fanotify(u32 response);
> +extern void __audit_fanotify(u32 response, struct
> fanotify_response_info_audit_rule *friar); extern void
> __audit_tk_injoffset(struct timespec64 offset);
>  extern void __audit_ntp_log(const struct audit_ntp_data *ad);
>  extern void __audit_log_nfcfg(const char *name, u8 af, unsigned int
> nentries, @@ -523,10 +524,10 @@ static inline void
> audit_log_kern_module(char *name) __audit_log_kern_module(name);
>  }
> 
> -static inline void audit_fanotify(u32 response)
> +static inline void audit_fanotify(u32 response, struct
> fanotify_response_info_audit_rule *friar) {
>  	if (!audit_dummy_context())
> -		__audit_fanotify(response);
> +		__audit_fanotify(response, friar);
>  }
> 
>  static inline void audit_tk_injoffset(struct timespec64 offset)
> @@ -679,7 +680,7 @@ static inline void audit_log_kern_module(char *name)
>  {
>  }
> 
> -static inline void audit_fanotify(u32 response)
> +static inline void audit_fanotify(u32 response, struct
> fanotify_response_info_audit_rule *friar) { }
> 
>  static inline void audit_tk_injoffset(struct timespec64 offset)
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index d1fb821de104..8d523066d81f 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -64,6 +64,7 @@
>  #include <uapi/linux/limits.h>
>  #include <uapi/linux/netfilter/nf_tables.h>
>  #include <uapi/linux/openat2.h> // struct open_how
> +#include <uapi/linux/fanotify.h>
> 
>  #include "audit.h"
> 
> @@ -2877,10 +2878,28 @@ void __audit_log_kern_module(char *name)
>  	context->type = AUDIT_KERN_MODULE;
>  }
> 
> -void __audit_fanotify(u32 response)
> +void __audit_fanotify(u32 response, struct
> fanotify_response_info_audit_rule *friar) {
> -	audit_log(audit_context(), GFP_KERNEL,
> -		AUDIT_FANOTIFY,	"resp=%u", response);
> +	struct audit_context *ctx = audit_context();
> +	struct audit_buffer *ab;
> +	char numbuf[12];
> +
> +	if (friar->hdr.type == FAN_RESPONSE_INFO_NONE) {
> +		audit_log(audit_context(), GFP_KERNEL, AUDIT_FANOTIFY,
> +			  "resp=%u fan_type=%u fan_info=3F subj_trust=2 
obj_trust=2",
> +			  response, FAN_RESPONSE_INFO_NONE);
> +		return;
> +	}
> +	ab = audit_log_start(ctx, GFP_KERNEL, AUDIT_FANOTIFY);
> +	if (ab) {
> +		audit_log_format(ab, "resp=%u fan_type=%u fan_info=",
> +				 response, friar->hdr.type);
> +		snprintf(numbuf, sizeof(numbuf), "%u", friar->rule_number);
> +		audit_log_n_hex(ab, numbuf, sizeof(numbuf));

I don't think it needs to be converted to ascii and then hexencoded. As Paul 
said, probably %X is all we need here.

-Steve


> +		audit_log_format(ab, " subj_trust=%u obj_trust=%u",
> +				 friar->subj_trust, friar->obj_trust);
> +		audit_log_end(ab);
> +	}
>  }
> 
>  void __audit_tk_injoffset(struct timespec64 offset)