[PATCH ghak8 ALT4 V4 1/3] audit: show partial pathname for entries with anonymous parents

[Richard Guy Briggs]

Tracefs or debugfs were causing hundreds to thousands of null PATH
records to be associated with the init_module and finit_module SYSCALL
records on a few modules when the following rule was in place for
startup:
        -a always,exit -F arch=x86_64 -S init_module -F key=mod-load

This happens because the parent inode is not found in the task's
audit_names list and hence treats it as anonymous.  This gives us no
information other than a numerical device number for a device that may
no longer be visible upon log inspeciton, and an inode number.

Fill in the partial known pathname from the filesystem mount point to
the leaf node on previously null PATH records from entries that have an
anonymous parent from the child dentry using dentry_path_raw().

Make the dentry argument of __audit_inode_child() non-const so that we
can take a reference to it in the case of an anonymous parent with
dget() and dget_parent() to be able to later print a partial path from
the host filesystem rather than null.

Since all we are given is an inode of the parent and the dentry of the
child, finding the path from the mount point to the root of the
filesystem is more challenging that would involve searching all
vfsmounts from "/" until a matching dentry is found for that
filesystem's root dentry.  Even if one is found, there may be more than
one mount point.  At this point the gain seems marginal since
knowing the filesystem type and path are a significant help in tracking
down the source of the PATH records and being able to address them.

Sample output:
type=PROCTITLE msg=audit(1488317694.446:143): proctitle=2F7362696E2F6D6F6470726F6265002D71002D2D006E66737634
type=PATH msg=audit(1488317694.446:143): item=797 name=events/nfs4/nfs4_setclientid/format inode=15969 dev=00:09 mode=0100444 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:tracefs_t:s0 nametype=CREATE cap_fp=0000000000000000 cap_fi=0000000000000000 cap_fe=0 cap_fver=0
type=PATH msg=audit(1488317694.446:143): item=796 name=events/nfs4/nfs4_setclientid inode=15964 dev=00:09 mode=040755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:tracefs_t:s0 nametype=PARENT cap_fp=0000000000000000 cap_fi=0000000000000000 cap_fe=0 cap_fver=0
...
type=PATH msg=audit(1488317694.446:143): item=1 name=events/nfs4 inode=15571 dev=00:09 mode=040755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:tracefs_t:s0 nametype=CREATE cap_fp=0000000000000000 cap_fi=0000000000000000 cap_fe=0 cap_fver=0
type=PATH msg=audit(1488317694.446:143): item=0 name=events inode=119 dev=00:09 mode=040755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:tracefs_t:s0 nametype=PARENT cap_fp=0000000000000000 cap_fi=0000000000000000 cap_fe=0 cap_fver=0
type=KERN_MODULE msg=audit(1488317694.446:143): name="nfsv4"
type=SYSCALL msg=audit(1488317694.446:143): arch=c000003e syscall=313 success=yes exit=0 a0=1 a1=55d5a35ce106 a2=0 a3=1 items=798 ppid=6 pid=528 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="modprobe" exe="/usr/bin/kmod" subj=system_u:system_r:insmod_t:s0 key="mod-load"

See: https://github.com/linux-audit/audit-kernel/issues/8
Test case: https://github.com/linux-audit/audit-testsuite/issues/42

Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>

---
v4:
  fix fullpath memleak
  switch from log_format() to audit_log_untrustedstring()
  remove leading / from pathname relative to unknown mount point

v3:
  fix audit_buffer leak and dname error allocation leak audit_log_name
  only put audit_name->dentry if it is being replaced

v2:
  deconstify struct dentry*
  add hex prefix to fstype
---
 include/linux/audit.h |  8 ++++----
 kernel/audit.c        | 28 +++++++++++++++++++++++++++-
 kernel/audit.h        |  1 +
 kernel/auditsc.c      |  8 +++++++-
 4 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/include/linux/audit.h b/include/linux/audit.h
index af410d9..2020f1d 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -232,7 +232,7 @@ extern void __audit_inode(struct filename *name, const struct dentry *dentry,
 				unsigned int flags);
 extern void __audit_file(const struct file *);
 extern void __audit_inode_child(struct inode *parent,
-				const struct dentry *dentry,
+				struct dentry *dentry,
 				const unsigned char type);
 extern void __audit_seccomp(unsigned long syscall, long signr, int code);
 extern void __audit_ptrace(struct task_struct *t);
@@ -297,7 +297,7 @@ static inline void audit_inode_parent_hidden(struct filename *name,
 				AUDIT_INODE_PARENT | AUDIT_INODE_HIDDEN);
 }
 static inline void audit_inode_child(struct inode *parent,
-				     const struct dentry *dentry,
+				     struct dentry *dentry,
 				     const unsigned char type) {
 	if (unlikely(!audit_dummy_context()))
 		__audit_inode_child(parent, dentry, type);
@@ -481,7 +481,7 @@ static inline void __audit_inode(struct filename *name,
 					unsigned int flags)
 { }
 static inline void __audit_inode_child(struct inode *parent,
-					const struct dentry *dentry,
+					struct dentry *dentry,
 					const unsigned char type)
 { }
 static inline void audit_inode(struct filename *name,
@@ -495,7 +495,7 @@ static inline void audit_inode_parent_hidden(struct filename *name,
 				const struct dentry *dentry)
 { }
 static inline void audit_inode_child(struct inode *parent,
-				     const struct dentry *dentry,
+				     struct dentry *dentry,
 				     const unsigned char type)
 { }
 static inline void audit_core_dumps(long signr)
diff --git a/kernel/audit.c b/kernel/audit.c
index 227db99..0c8d5a8 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -72,6 +72,7 @@
 #include <linux/freezer.h>
 #include <linux/pid_namespace.h>
 #include <net/netns/generic.h>
+#include <linux/dcache.h>
 
 #include "audit.h"
 
@@ -2056,6 +2057,10 @@ void audit_copy_inode(struct audit_names *name, const struct dentry *dentry,
 	name->gid   = inode->i_gid;
 	name->rdev  = inode->i_rdev;
 	security_inode_getsecid(inode, &name->osid);
+	if (name->dentry) {
+		dput(name->dentry);
+		name->dentry = NULL;
+	}
 	audit_copy_fcaps(name, dentry);
 }
 
@@ -2097,8 +2102,29 @@ void audit_log_name(struct audit_context *context, struct audit_names *n,
 			audit_log_n_untrustedstring(ab, n->name->name,
 						    n->name_len);
 		}
-	} else
+	} else if (n->dentry) {
+		char *fullpath;
+		const char *fullpathp = NULL;
+
+		fullpath = kmalloc(PATH_MAX, GFP_KERNEL);
+		if (fullpath) {
+			fullpathp = dentry_path_raw(n->dentry, fullpath, PATH_MAX);
+			if (IS_ERR(fullpathp)) {
+				fullpathp = NULL;
+			} else {
+				while (*fullpathp == '/')
+					fullpathp++;
+				if (*fullpathp == 0)
+					fullpathp = NULL;
+			}
+		}
+		audit_log_format(ab, " name=");
+		audit_log_untrustedstring(ab, fullpathp ?: "?");
+		if (fullpath)
+			kfree(fullpath);
+	} else {
 		audit_log_format(ab, " name=(null)");
+	}
 
 	if (n->ino != AUDIT_INO_UNSET)
 		audit_log_format(ab, " inode=%lu"
diff --git a/kernel/audit.h b/kernel/audit.h
index af5bc59..81f6865 100644
--- a/kernel/audit.h
+++ b/kernel/audit.h
@@ -85,6 +85,7 @@ struct audit_names {
 
 	unsigned long		ino;
 	dev_t			dev;
+	struct dentry		*dentry;
 	umode_t			mode;
 	kuid_t			uid;
 	kgid_t			gid;
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index e80459f..b73ede0 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -75,6 +75,7 @@
 #include <linux/uaccess.h>
 #include <linux/fsnotify_backend.h>
 #include <uapi/linux/limits.h>
+#include <linux/dcache.h>
 
 #include "audit.h"
 
@@ -882,6 +883,8 @@ static inline void audit_free_names(struct audit_context *context)
 		list_del(&n->list);
 		if (n->name)
 			putname(n->name);
+		if (n->dentry)
+			dput(n->dentry);
 		if (n->should_free)
 			kfree(n);
 	}
@@ -1862,7 +1865,7 @@ void __audit_file(const struct file *file)
  * unsuccessful attempts.
  */
 void __audit_inode_child(struct inode *parent,
-			 const struct dentry *dentry,
+			 struct dentry *dentry,
 			 const unsigned char type)
 {
 	struct audit_context *context = current->audit_context;
@@ -1941,6 +1944,7 @@ void __audit_inode_child(struct inode *parent,
 		if (!n)
 			return;
 		audit_copy_inode(n, NULL, parent);
+		n->dentry = dget_parent(dentry);
 	}
 
 	if (!found_child) {
@@ -1962,6 +1966,8 @@ void __audit_inode_child(struct inode *parent,
 		audit_copy_inode(found_child, dentry, inode);
 	else
 		found_child->ino = AUDIT_INO_UNSET;
+	if (!found_parent)
+		found_child->dentry = dget(dentry);
 }
 EXPORT_SYMBOL_GPL(__audit_inode_child);
 
-- 
1.8.3.1