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Date: Fri, 14 Feb 2020 10:42:54 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: Stephen Smalley <sds@...ho.nsa.gov>, Will Deacon <will@...nel.org>,
Al Viro <viro@...iv.linux.org.uk>,
Paul Moore <paul@...l-moore.com>,
Sasha Levin <sashal@...nel.org>, selinux@...r.kernel.org
Subject: [PATCH AUTOSEL 5.5 182/542] selinux: fall back to ref-walk if audit is required
From: Stephen Smalley <sds@...ho.nsa.gov>
[ Upstream commit 0188d5c025ca8fe756ba3193bd7d150139af5a88 ]
commit bda0be7ad994 ("security: make inode_follow_link RCU-walk aware")
passed down the rcu flag to the SELinux AVC, but failed to adjust the
test in slow_avc_audit() to also return -ECHILD on LSM_AUDIT_DATA_DENTRY.
Previously, we only returned -ECHILD if generating an audit record with
LSM_AUDIT_DATA_INODE since this was only relevant from inode_permission.
Move the handling of MAY_NOT_BLOCK to avc_audit() and its inlined
equivalent in selinux_inode_permission() immediately after we determine
that audit is required, and always fall back to ref-walk in this case.
Fixes: bda0be7ad994 ("security: make inode_follow_link RCU-walk aware")
Reported-by: Will Deacon <will@...nel.org>
Suggested-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Stephen Smalley <sds@...ho.nsa.gov>
Signed-off-by: Paul Moore <paul@...l-moore.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
security/selinux/avc.c | 24 +++++-------------------
security/selinux/hooks.c | 11 +++++++----
security/selinux/include/avc.h | 8 +++++---
3 files changed, 17 insertions(+), 26 deletions(-)
diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index 74c43ebe34bb8..23dc888ae3056 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -424,7 +424,7 @@ static inline int avc_xperms_audit(struct selinux_state *state,
if (likely(!audited))
return 0;
return slow_avc_audit(state, ssid, tsid, tclass, requested,
- audited, denied, result, ad, 0);
+ audited, denied, result, ad);
}
static void avc_node_free(struct rcu_head *rhead)
@@ -758,8 +758,7 @@ static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
noinline int slow_avc_audit(struct selinux_state *state,
u32 ssid, u32 tsid, u16 tclass,
u32 requested, u32 audited, u32 denied, int result,
- struct common_audit_data *a,
- unsigned int flags)
+ struct common_audit_data *a)
{
struct common_audit_data stack_data;
struct selinux_audit_data sad;
@@ -772,17 +771,6 @@ noinline int slow_avc_audit(struct selinux_state *state,
a->type = LSM_AUDIT_DATA_NONE;
}
- /*
- * When in a RCU walk do the audit on the RCU retry. This is because
- * the collection of the dname in an inode audit message is not RCU
- * safe. Note this may drop some audits when the situation changes
- * during retry. However this is logically just as if the operation
- * happened a little later.
- */
- if ((a->type == LSM_AUDIT_DATA_INODE) &&
- (flags & MAY_NOT_BLOCK))
- return -ECHILD;
-
sad.tclass = tclass;
sad.requested = requested;
sad.ssid = ssid;
@@ -855,16 +843,14 @@ static int avc_update_node(struct selinux_avc *avc,
/*
* 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 cannot safely audit the denial. Otherwise,
+ * 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 in slow_avc_audit(), and the
- * logic in selinux_inode_follow_link and selinux_inode_permission
- * for the VFS MAY_NOT_BLOCK flag, which is transliterated into
- * AVC_NONBLOCKING for avc_has_perm_noaudit().
+ * See the corresponding handling of MAY_NOT_BLOCK in avc_audit()
+ * and selinux_inode_permission().
*/
if (flags & AVC_NONBLOCKING)
return 0;
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 710a4fffa66f4..65641c61ecb94 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3011,8 +3011,7 @@ static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode,
static noinline int audit_inode_permission(struct inode *inode,
u32 perms, u32 audited, u32 denied,
- int result,
- unsigned flags)
+ int result)
{
struct common_audit_data ad;
struct inode_security_struct *isec = selinux_inode(inode);
@@ -3023,7 +3022,7 @@ static noinline int audit_inode_permission(struct inode *inode,
rc = slow_avc_audit(&selinux_state,
current_sid(), isec->sid, isec->sclass, perms,
- audited, denied, result, &ad, flags);
+ audited, denied, result, &ad);
if (rc)
return rc;
return 0;
@@ -3070,7 +3069,11 @@ static int selinux_inode_permission(struct inode *inode, int mask)
if (likely(!audited))
return rc;
- rc2 = audit_inode_permission(inode, perms, audited, denied, rc, flags);
+ /* fall back to ref-walk if we have to generate audit */
+ if (flags & MAY_NOT_BLOCK)
+ return -ECHILD;
+
+ rc2 = audit_inode_permission(inode, perms, audited, denied, rc);
if (rc2)
return rc2;
return rc;
diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
index 74ea50977c201..cf4cc3ef959b5 100644
--- a/security/selinux/include/avc.h
+++ b/security/selinux/include/avc.h
@@ -100,8 +100,7 @@ static inline u32 avc_audit_required(u32 requested,
int slow_avc_audit(struct selinux_state *state,
u32 ssid, u32 tsid, u16 tclass,
u32 requested, u32 audited, u32 denied, int result,
- struct common_audit_data *a,
- unsigned flags);
+ struct common_audit_data *a);
/**
* avc_audit - Audit the granting or denial of permissions.
@@ -135,9 +134,12 @@ 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, flags);
+ a);
}
#define AVC_STRICT 1 /* Ignore permissive mode. */
--
2.20.1
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