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

On 2023-01-09 19:06, Steve Grubb wrote:

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.

I'll have a closer look, because this wasn't the intended behaviour.

On Monday, December 12, 2022 9:06:11 AM EST Richard Guy Briggs wrote:

quoted

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...

Well, it *is* 13 decimal, expressed as a hex-encoded string as was
requested for future-proofing, albeit longer than necessary...

quoted

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 [off-list ref].

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 <redacted>
Link: https://lore.kernel.org/r/3075502.aeNJFYEL58@x2 (local)
Signed-off-by: Richard Guy Briggs <redacted>
---
 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",

quoted

+			  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

quoted

+		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)

- RGB

--
Richard Guy Briggs [off-list ref]
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