[followup to dump_common_audit_data() changes from this winter; in vfs.git#work.audit]
Does anybody have objections to the below?
>From 663a40ab49308b5acaba8a335190fce66e17d969 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Sat, 16 Jan 2021 15:40:54 -0500
Subject: [PATCH 1/2] selinux: slow_avc_audit has become non-blocking
dump_common_audit_data() is safe to use under rcu_read_lock() now;
no need for AVC_NONBLOCKING and games around it
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
security/selinux/avc.c | 28 ++++++++--------------------
security/selinux/hooks.c | 13 ++-----------
security/selinux/include/avc.h | 4 ----
3 files changed, 10 insertions(+), 35 deletions(-)
diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index ad451cf9375e..9c3d2a29616a 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -758,7 +758,11 @@ static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
}
}
-/* This is the slow part of avc audit with big stack footprint */
+/*
+ * This is the slow part of avc audit with big stack footprint.
+ * Note that it is non-blocking and can be called from under
+ * rcu_read_lock().
+ */
noinline int slow_avc_audit(struct selinux_state *state,
u32 ssid, u32 tsid, u16 tclass,
u32 requested, u32 audited, u32 denied, int result,
@@ -825,7 +829,7 @@ int __init avc_add_callback(int (*callback)(u32 event), u32 events)
* @ssid,@tsid,@tclass : identifier of an AVC entry
* @seqno : sequence number when decision was made
* @xpd: extended_perms_decision to be added to the node
- * @flags: the AVC_* flags, e.g. AVC_NONBLOCKING, AVC_EXTENDED_PERMS, or 0.
+ * @flags: the AVC_* flags, e.g. AVC_EXTENDED_PERMS, or 0.
*
* if a valid AVC entry doesn't exist,this function returns -ENOENT.
* if kmalloc() called internal returns NULL, this function returns -ENOMEM.
@@ -844,21 +848,6 @@ static int avc_update_node(struct selinux_avc *avc,
struct hlist_head *head;
spinlock_t *lock;
- /*
- * If we are in a non-blocking code path, e.g. VFS RCU walk,
- * then we must not add permissions to a cache entry
- * because we will not audit the denial. Otherwise,
- * during the subsequent blocking retry (e.g. VFS ref walk), we
- * will find the permissions already granted in the cache entry
- * and won't audit anything at all, leading to silent denials in
- * permissive mode that only appear when in enforcing mode.
- *
- * See the corresponding handling of MAY_NOT_BLOCK in avc_audit()
- * and selinux_inode_permission().
- */
- if (flags & AVC_NONBLOCKING)
- return 0;
-
node = avc_alloc_node(avc);
if (!node) {
rc = -ENOMEM;
@@ -1119,7 +1108,7 @@ int avc_has_extended_perms(struct selinux_state *state,
* @tsid: target security identifier
* @tclass: target security class
* @requested: requested permissions, interpreted based on @tclass
- * @flags: AVC_STRICT, AVC_NONBLOCKING, or 0
+ * @flags: AVC_STRICT or 0
* @avd: access vector decisions
*
* Check the AVC to determine whether the @requested permissions are granted
@@ -1204,8 +1193,7 @@ int avc_has_perm_flags(struct selinux_state *state,
struct av_decision avd;
int rc, rc2;
- rc = avc_has_perm_noaudit(state, ssid, tsid, tclass, requested,
- (flags & MAY_NOT_BLOCK) ? AVC_NONBLOCKING : 0,
+ rc = avc_has_perm_noaudit(state, ssid, tsid, tclass, requested, 0,
&avd);
rc2 = avc_audit(state, ssid, tsid, tclass, requested, &avd, rc,
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index eaea837d89d1..f22ad1229471 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3164,17 +3164,13 @@ static noinline int audit_inode_permission(struct inode *inode,
{
struct common_audit_data ad;
struct inode_security_struct *isec = selinux_inode(inode);
- int rc;
ad.type = LSM_AUDIT_DATA_INODE;
ad.u.inode = inode;
- rc = slow_avc_audit(&selinux_state,
+ return slow_avc_audit(&selinux_state,
current_sid(), isec->sid, isec->sclass, perms,
audited, denied, result, &ad);
- if (rc)
- return rc;
- return 0;
}
static int selinux_inode_permission(struct inode *inode, int mask)
@@ -3209,8 +3205,7 @@ static int selinux_inode_permission(struct inode *inode, int mask)
return PTR_ERR(isec);
rc = avc_has_perm_noaudit(&selinux_state,
- sid, isec->sid, isec->sclass, perms,
- no_block ? AVC_NONBLOCKING : 0,
+ sid, isec->sid, isec->sclass, perms, 0,
&avd);
audited = avc_audit_required(perms, &avd, rc,
from_access ? FILE__AUDIT_ACCESS : 0,
@@ -3218,10 +3213,6 @@ static int selinux_inode_permission(struct inode *inode, int mask)
if (likely(!audited))
return rc;
- /* fall back to ref-walk if we have to generate audit */
- if (no_block)
- return -ECHILD;
-
rc2 = audit_inode_permission(inode, perms, audited, denied, rc);
if (rc2)
return rc2;
diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
index cf4cc3ef959b..c3bbfc8e8b46 100644
--- a/security/selinux/include/avc.h
+++ b/security/selinux/include/avc.h
@@ -134,9 +134,6 @@ static inline int avc_audit(struct selinux_state *state,
audited = avc_audit_required(requested, avd, result, 0, &denied);
if (likely(!audited))
return 0;
- /* fall back to ref-walk if we have to generate audit */
- if (flags & MAY_NOT_BLOCK)
- return -ECHILD;
return slow_avc_audit(state, ssid, tsid, tclass,
requested, audited, denied, result,
a);
@@ -144,7 +141,6 @@ static inline int avc_audit(struct selinux_state *state,
#define AVC_STRICT 1 /* Ignore permissive mode. */
#define AVC_EXTENDED_PERMS 2 /* update extended permissions */
-#define AVC_NONBLOCKING 4 /* non blocking */
int avc_has_perm_noaudit(struct selinux_state *state,
u32 ssid, u32 tsid,
u16 tclass, u32 requested,
--
2.11.0
