[PATCH] lsm,audit,selinux: Introduce a new audit data type LSM_AUDIT_DATA_FILE

[Vivek Goyal]

Hi,

Right now LSM_AUDIT_DATA_PATH type contains "struct path" in union "u" of
common_audit_data. This information is used to print path of file 
at the same time it is also used to get to dentry and inode. And this
inode information is used to get to superblock and device and print
device information.

This does not work well for layered filesystems like overlay where dentry
contained in path is overlay dentry and not the real dentry of underlying
file system. That means inode retrieved from dentry is also overlay
inode and not the real inode.

seliux helpers like file_path_has_perm() are doing checks on inode retrieved
from file_inode(). This returns the real inode and not the overlay inode.
That means we are doing check on real inode but for audit purposes we
are printing details of overlay inode and that can be confusing while
debugging.

Hence, introduce a new type LSM_AUDIT_DATA_FILE which carries file
information and inode retrieved is real inode using file_inode(). That
way right avc denied information is given to user.

For example, following is one example avc before the patch. 

type=AVC msg=audit(1473360868.399:214): avc:  denied  { read open } for  pid=1765 comm="cat" path="/root/git/selinux-testsuite/tests/overlay/container1/merged/readfile" dev="overlay" ino=21443 scontext=unconfined_u:unconfined_r:test_overlay_client_t:s0:c10,c20 tcontext=unconfined_u:object_r:test_overlay_files_ro_t:s0 tclass=file permissive=0

It looks as follows after the patch.

type=AVC msg=audit(1473360017.388:282): avc:  denied  { read open } for  pid=2530 comm="cat" path="/root/git/selinux-testsuite/tests/overlay/container1/merged/readfile" dev="dm-0" ino=2377915 scontext=unconfined_u:unconfined_r:test_overlay_client_t:s0:c10,c20 tcontext=unconfined_u:object_r:test_overlay_files_ro_t:s0 tclass=file permissive=0 

Notice that now dev information points to "dm-0" device instead of "overlay"
device. This makes it clear that check failed on underlying inode and not
on the overlay inode.

Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
---
 include/linux/lsm_audit.h |    2 ++
 security/lsm_audit.c      |   13 +++++++++++++
 security/selinux/hooks.c  |   16 ++++++++--------
 3 files changed, 23 insertions(+), 8 deletions(-)

Index: pcmoore-linux/include/linux/lsm_audit.h
===================================================================
--- pcmoore-linux.orig/include/linux/lsm_audit.h	2016-09-08 14:56:10.173159741 -0400
+++ pcmoore-linux/include/linux/lsm_audit.h	2016-09-08 14:56:14.066159741 -0400
@@ -59,6 +59,7 @@ struct common_audit_data {
 #define LSM_AUDIT_DATA_INODE	9
 #define LSM_AUDIT_DATA_DENTRY	10
 #define LSM_AUDIT_DATA_IOCTL_OP	11
+#define LSM_AUDIT_DATA_FILE	12
 	union 	{
 		struct path path;
 		struct dentry *dentry;
@@ -75,6 +76,7 @@ struct common_audit_data {
 #endif
 		char *kmod_name;
 		struct lsm_ioctlop_audit *op;
+		struct file *file;
 	} u;
 	/* this union contains LSM specific data */
 	union {
Index: pcmoore-linux/security/lsm_audit.c
===================================================================
--- pcmoore-linux.orig/security/lsm_audit.c	2016-09-08 14:56:10.173159741 -0400
+++ pcmoore-linux/security/lsm_audit.c	2016-09-08 14:56:14.067159741 -0400
@@ -245,6 +245,19 @@ static void dump_common_audit_data(struc
 		}
 		break;
 	}
+	case LSM_AUDIT_DATA_FILE: {
+		struct inode *inode;
+
+		audit_log_d_path(ab, " path=", &a->u.file->f_path);
+
+		inode = file_inode(a->u.file);
+		if (inode) {
+			audit_log_format(ab, " dev=");
+			audit_log_untrustedstring(ab, inode->i_sb->s_id);
+			audit_log_format(ab, " ino=%lu", inode->i_ino);
+		}
+		break;
+	}
 	case LSM_AUDIT_DATA_IOCTL_OP: {
 		struct inode *inode;
 
Index: pcmoore-linux/security/selinux/hooks.c
===================================================================
--- pcmoore-linux.orig/security/selinux/hooks.c	2016-09-08 14:56:10.173159741 -0400
+++ pcmoore-linux/security/selinux/hooks.c	2016-09-09 09:15:37.001159741 -0400
@@ -1761,8 +1761,8 @@ static inline int file_path_has_perm(con
 {
 	struct common_audit_data ad;
 
-	ad.type = LSM_AUDIT_DATA_PATH;
-	ad.u.path = file->f_path;
+	ad.type = LSM_AUDIT_DATA_FILE;
+	ad.u.file = file;
 	return inode_has_perm(cred, file_inode(file), av, &ad);
 }
 
@@ -1784,8 +1784,8 @@ static int file_has_perm(const struct cr
 	u32 sid = cred_sid(cred);
 	int rc;
 
-	ad.type = LSM_AUDIT_DATA_PATH;
-	ad.u.path = file->f_path;
+	ad.type = LSM_AUDIT_DATA_FILE;
+	ad.u.file = file;
 
 	if (sid != fsec->sid) {
 		rc = avc_has_perm(sid, fsec->sid,
@@ -2365,8 +2365,8 @@ static int selinux_bprm_set_creds(struct
 			new_tsec->sid = old_tsec->sid;
 	}
 
-	ad.type = LSM_AUDIT_DATA_PATH;
-	ad.u.path = bprm->file->f_path;
+	ad.type = LSM_AUDIT_DATA_FILE;
+	ad.u.file = bprm->file;
 
 	if (new_tsec->sid == old_tsec->sid) {
 		rc = avc_has_perm(old_tsec->sid, isec->sid,
@@ -3833,8 +3833,8 @@ static int selinux_kernel_module_from_fi
 
 	/* finit_module */
 
-	ad.type = LSM_AUDIT_DATA_PATH;
-	ad.u.path = file->f_path;
+	ad.type = LSM_AUDIT_DATA_FILE;
+	ad.u.file = file;
 
 	fsec = file->f_security;
 	if (sid != fsec->sid) {