[PATCH 3/3] SMACK: Make smack directory access check RCU safe

Andi Kleen
2011-04-22T00:24:13Z

From: Andi Kleen <ak@linux.intel.com>

SMACK already uses RCU internally, so except for auditing,
it's safe to not abort a RCU dcache walk.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
security/smack/smack.h | 14 ++++++++++++--
security/smack/smack_access.c | 26 ++++++++++++++++++++------
security/smack/smack_lsm.c | 5 +----
3 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/security/smack/smack.h b/security/smack/smack.h
index b449cfd..0cc17e3 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -198,8 +198,18 @@ struct inode_smack *new_inode_smack(char *);
* These functions are in smack_access.c
*/
int smk_access_entry(char *, char *, struct list_head *);
-int smk_access(char *, char *, int, struct smk_audit_info *);
-int smk_curacc(char *, u32, struct smk_audit_info *);
+int smk_access_flags(char *, char *, int, struct smk_audit_info *, int);
+static inline int smk_access(char *a, char *b, int c, struct smk_audit_info *d)
+{
+ return smk_access_flags(a, b, c, d, 0);
+}
+int smk_curacc_flags(char *, u32, struct smk_audit_info *, int vfs_flags);
+
+static inline int smk_curacc(char *a, u32 b, struct smk_audit_info *c)
+{
+ return smk_curacc_flags(a, b, c, 0);
+}
+
int smack_to_cipso(const char *, struct smack_cipso *);
void smack_from_cipso(u32, char *, char *);
char *smack_from_secid(const u32);
diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index 9294c5d..43b20f3 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -128,8 +128,8 @@ int smk_access_entry(char *subject_label, char *object_label,
* will be on the list, so checking the pointers may be a worthwhile
* optimization.
*/
-int smk_access(char *subject_label, char *object_label, int request,
- struct smk_audit_info *a)
+int smk_access_flags(char *subject_label, char *object_label, int request,
+ struct smk_audit_info *a, int vfs_flags)
{
int may = MAY_NOT;
int rc = 0;
@@ -194,8 +194,17 @@ int smk_access(char *subject_label, char *object_label, int request,
rc = -EACCES;
out_audit:
#ifdef CONFIG_AUDIT
- if (a)
+ if (a) {
+ /*
+ * If we're in a RCU walk try again without RCU
+ * for auditing. While in theory this may skip
+ * auditing when things change logically it is
+ * just as if the operation succeeded a bit later.
+ */
+ if (vfs_flags & IPERM_FLAG_RCU)
+ return -ECHILD;
smack_log(subject_label, object_label, request, rc, a);
+ }
#endif
return rc;
}
@@ -211,7 +220,8 @@ out_audit:
* non zero otherwise. It allows that current may have the capability
* to override the rules.
*/
-int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
+int smk_curacc_flags(char *obj_label, u32 mode, struct smk_audit_info *a,
+ int vfs_flags)
{
struct task_smack *tsp = current_security();
char *sp = smk_of_task(tsp);
@@ -221,7 +231,7 @@ int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
/*
* Check the global rule list
*/
- rc = smk_access(sp, obj_label, mode, NULL);
+ rc = smk_access_flags(sp, obj_label, mode, NULL, vfs_flags);
if (rc == 0) {
/*
* If there is an entry in the task's rule list
@@ -248,8 +258,12 @@ int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)

out_audit:
#ifdef CONFIG_AUDIT
- if (a)
+ if (a && rc != -ECHILD) {
+ /* Audit in non RCU mode */
+ if (vfs_flags & IPERM_FLAG_RCU)
+ return -ECHILD;
smack_log(sp, obj_label, mode, rc, a);
+ }
#endif
return rc;
}
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 400a5d5..366d250 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -697,12 +697,9 @@ static int smack_inode_permission(struct inode *inode, int mask, unsigned flags)
if (mask == 0)
return 0;

- /* May be droppable after audit */
- if (flags & IPERM_FLAG_RCU)
- return -ECHILD;
smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_FS);
smk_ad_setfield_u_fs_inode(&ad, inode);
- return smk_curacc(smk_of_inode(inode), mask, &ad);
+ return smk_curacc_flags(smk_of_inode(inode), mask, &ad, flags);
}

/**
--
1.7.4.2