[RFC,v2,2/2] selinux: stop passing MAY_NOT_BLOCK to the AVC upon follow_link

Commit Message

Stephen Smalley Dec. 7, 2018, 4:23 p.m. UTC

commit bda0be7ad9948 ("security: make inode_follow_link RCU-walk aware")
switched selinux_inode_follow_link() to use avc_has_perm_flags() and
pass down the MAY_NOT_BLOCK flag if called during RCU walk.  However,
the only test of MAY_NOT_BLOCK occurs during slow_avc_audit()
and only if passing an inode as audit data (LSM_AUDIT_DATA_INODE).  Since
selinux_inode_follow_link() passes a dentry directly, passing MAY_NOT_BLOCK
here serves no purpose.  Switch selinux_inode_follow_link() to use
avc_has_perm() and drop avc_has_perm_flags() since there are no other
users.

Signed-off-by: Stephen Smalley <[e-mail]>
---
This patch should wait on confirmation from the vfs folks that we really
only need to return ECHILD in the LSM_AUDIT_DATA_INODE case and not the
LSM_AUDIT_DATA_DENTRY case.

 security/selinux/avc.c         | 19 -------------------
 security/selinux/hooks.c       |  5 ++---
 security/selinux/include/avc.h |  5 -----
 3 files changed, 2 insertions(+), 27 deletions(-)

Patch

diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index 5de18a6d5c3f..a89b306d8069 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -1209,25 +1209,6 @@  int avc_has_perm(struct selinux_state *state, u32 ssid, u32 tsid, u16 tclass,
 	return rc;
 }
 
-int avc_has_perm_flags(struct selinux_state *state,
-		       u32 ssid, u32 tsid, u16 tclass, u32 requested,
-		       struct common_audit_data *auditdata,
-		       int flags)
-{
-	struct av_decision avd;
-	int rc, rc2;
-
-	rc = avc_has_perm_noaudit(state, ssid, tsid, tclass, requested,
-				  (flags & MAY_NOT_BLOCK) ? AVC_NONBLOCKING : 0,
-				  &avd);
-
-	rc2 = avc_audit(state, ssid, tsid, tclass, requested, &avd, rc,
-			auditdata, flags);
-	if (rc2)
-		return rc2;
-	return rc;
-}
-
 u32 avc_policy_seqno(struct selinux_state *state)
 {
 	return state->avc->avc_cache.latest_notif;
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 9b05f84808d9..f012d2eb159e 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3139,9 +3139,8 @@  static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode,
 	if (IS_ERR(isec))
 		return PTR_ERR(isec);
 
-	return avc_has_perm_flags(&selinux_state,
-				  sid, isec->sid, isec->sclass, FILE__READ, &ad,
-				  rcu ? MAY_NOT_BLOCK : 0);
+	return avc_has_perm(&selinux_state,
+			    sid, isec->sid, isec->sclass, FILE__READ, &ad);
 }
 
 static noinline int audit_inode_permission(struct inode *inode,
diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
index 74ea50977c20..7be0e1e90e8b 100644
--- a/security/selinux/include/avc.h
+++ b/security/selinux/include/avc.h
@@ -153,11 +153,6 @@  int avc_has_perm(struct selinux_state *state,
 		 u32 ssid, u32 tsid,
 		 u16 tclass, u32 requested,
 		 struct common_audit_data *auditdata);
-int avc_has_perm_flags(struct selinux_state *state,
-		       u32 ssid, u32 tsid,
-		       u16 tclass, u32 requested,
-		       struct common_audit_data *auditdata,
-		       int flags);
 
 int avc_has_extended_perms(struct selinux_state *state,
 			   u32 ssid, u32 tsid, u16 tclass, u32 requested,