audit: address ANOM_LINK excess records

This V3 is a supplement to patches 1 and 2 of v1 already merged.

Audit link denied events were being unexpectedly produced in a disjoint way when audit was disabled, and when they were expected, there were duplicate PATH records. This patchset addresses both issues for symlinks and hardlinks.

This was introduced with

	commit b24a30a7305418ff138ff51776fc555ec57c011a
	("audit: fix event coverage of AUDIT_ANOM_LINK")
	commit a51d9eaa41866ab6b4b6ecad7b621f8b66ece0dc
	("fs: add link restriction audit reporting")

Here are the resulting events:

symlink:
type=PROCTITLE msg=audit(03/12/2018 02:21:49.578:310) : proctitle=ls ./my-passwd
type=PATH msg=audit(03/12/2018 02:21:49.578:310) : item=0 name=./my-passwd inode=17090 dev=00:27 mode=link,777 ouid=rgb ogid=rgb rdev=00:00 obj=unconfined_u:object_r:user_tmp_t:s0 nametype=NORMAL cap_fp=none cap_fi=none cap_fe=0 cap_fver=0
type=CWD msg=audit(03/12/2018 02:21:49.578:310) : cwd=/tmp
type=SYSCALL msg=audit(03/12/2018 02:21:49.578:310) : arch=x86_64 syscall=stat success=no exit=EACCES(Permission denied) a0=0x7ffd79950dda a1=0x563f658a03c8 a2=0x563f658a03c8 a3=0x79950d00 items=2 ppid=552 pid=629 auid=root uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=ttyS0 ses=1 comm=ls exe=/usr/bin/ls subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key=(null) type=ANOM_LINK msg=audit(03/12/2018 02:21:49.578:310) : op=follow_link ppid=552 pid=629 auid=root uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=ttyS0 ses=1 comm=ls exe=/usr/bin/ls subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 res=no
----
hardlink:
type=PROCTITLE msg=audit(03/12/2018 02:24:39.813:314) : proctitle=ln test test-ln
type=PATH msg=audit(03/12/2018 02:24:39.813:314) : item=1 name=/tmp inode=13529 dev=00:27 mode=dir,sticky,777 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:tmp_t:s0 nametype=PARENT cap_fp=none cap_fi=none cap_fe=0 cap_fver=0
type=PATH msg=audit(03/12/2018 02:24:39.813:314) : item=0 name=test inode=18112 dev=00:27 mode=file,700 ouid=root ogid=root rdev=00:00 obj=unconfined_u:object_r:user_tmp_t:s0 nametype=NORMAL cap_fp=none cap_fi=none cap_fe=0 cap_fver=0
type=CWD msg=audit(03/12/2018 02:24:39.813:314) : cwd=/tmp
type=SYSCALL msg=audit(03/12/2018 02:24:39.813:314) : arch=x86_64 syscall=linkat success=no exit=EPERM(Operation not permitted) a0=0xffffff9c a1=0x7ffccba77629 a2=0xffffff9c a3=0x7ffccba7762e items=2 ppid=605 pid=638 auid=rgb uid=rgb gid=rgb euid=rgb suid=rgb fsuid=rgb egid=rgb sgid=rgb fsgid=rgb tty=pts0 ses=4 comm=ln exe=/usr/bin/ln subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key=(null) type=ANOM_LINK msg=audit(03/12/2018 02:24:39.813:314) : op=linkat ppid=605 pid=638 auid=rgb uid=rgb gid=rgb euid=rgb suid=rgb fsuid=rgb egid=rgb sgid=rgb fsgid=rgb tty=pts0 ses=4 comm=ln exe=/usr/bin/ln subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 res=no

See: https://github.com/linux-audit/audit-kernel/issues/21
See also: https://github.com/linux-audit/audit-kernel/issues/51

Changelog:
v3:
- rebase on previously accepted 1/4 and 2/4 patches and drop them
- drop parent record audit_log_symlink_denied()
v2:
- remove now supperfluous struct path * parameter from audit_log_link_denied()
- refactor audit_log_symlink_denied() to properly free memory (pathname, filename)

Richard Guy Briggs (2):
audit: remove path param from link denied function
audit: add refused symlink to audit_names

 fs/namei.c            | 3 ++-
 include/linux/audit.h | 6 ++----
 kernel/audit.c        | 3 +--
 3 files changed, 5 insertions(+), 7 deletions(-)

1.8.3.1

In commit 45b578fe4c3cade6f4ca1fc934ce199afd857edc ("audit: link denied should not directly generate PATH record") the need for the struct path *link parameter was removed. Remove the now useless struct path argument.

---
 fs/namei.c            | 2 +-
 include/linux/audit.h | 6 ++----
 kernel/audit.c        | 3 +--
 3 files changed, 4 insertions(+), 7 deletions(-)

index 9cc91fb..50d2533 100644
@@ -1011,7 +1011,7 @@ static int may_linkat(struct path *link)
 	if (safe_hardlink_source(inode) || inode_owner_or_capable(inode))
 		return 0;
 
-	audit_log_link_denied("linkat", link);
+	audit_log_link_denied("linkat");
 	return -EPERM;
 }
 

index af410d9..75d5b03 100644
@@ -146,8 +146,7 @@ extern void		    audit_log_d_path(struct audit_buffer *ab,
 					     const struct path *path);
 extern void		    audit_log_key(struct audit_buffer *ab,
 					  char *key);
-extern void		    audit_log_link_denied(const char *operation,
-						  const struct path *link);
+extern void		    audit_log_link_denied(const char *operation);
 extern void		    audit_log_lost(const char *message);
 
 extern int audit_log_task_context(struct audit_buffer *ab);

@@ -194,8 +193,7 @@ static inline void audit_log_d_path(struct audit_buffer *ab,
 { }
 static inline void audit_log_key(struct audit_buffer *ab, char *key)
 { }
-static inline void audit_log_link_denied(const char *string,
-					 const struct path *link)
+static inline void audit_log_link_denied(const char *string)
 { }
 static inline int audit_log_task_context(struct audit_buffer *ab)
 {

index 3f2f143..e8bf8d7 100644
@@ -2308,9 +2308,8 @@ void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
 /**
  * audit_log_link_denied - report a link restriction denial
  * @operation: specific link operation
- * @link: the path that triggered the restriction
  */
-void audit_log_link_denied(const char *operation, const struct path *link)
+void audit_log_link_denied(const char *operation)
 {
 	struct audit_buffer *ab;
 

1.8.3.1

Audit link denied events for symlinks had duplicate PATH records rather than just updating the existing PATH record. Update the symlink's PATH record with the current dentry and inode information.

See: https://github.com/linux-audit/audit-kernel/issues/21

---
 fs/namei.c | 1 +
 1 file changed, 1 insertion(+)

index 50d2533..00f5041 100644
@@ -945,6 +945,7 @@ static inline int may_follow_link(struct nameidata *nd)
 	if (nd->flags & LOOKUP_RCU)
 		return -ECHILD;
 
+	audit_inode(nd->name, nd->stack[0].link.dentry, 0);
 	audit_log_link_denied("follow_link", &nd->stack[0].link);
 	return -EACCES;
 }

1.8.3.1

As far as your view is concerned it wasn't. It was compiled and tested, but the fix ended up in the following patch in the branch that wasn't included in this patchset so it effectively failed this bisection test. The sample records were copied from the test and not cooked. git add -p and/or git rebase -i fumble.

I'm very sorry to have wasted your time. I know it is precious right now.

- RGB

--
Richard Guy Briggs <[email protected]>
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