Merge tag 'lsm-pr-20240715' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/lsm

Pull lsm updates from Paul Moore:
 "Two LSM patches focused on cleaning up the inode xattr capability
  handling"

* tag 'lsm-pr-20240715' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/lsm:
  selinux,smack: remove the capability checks in the removexattr hooks
  lsm: fixup the inode xattr capability handling

4 files changed, 101 insertions, 42 deletions

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 44488b1ab9a9..855db460e08b 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -144,6 +144,7 @@ LSM_HOOK(int, 0, inode_setattr, struct mnt_idmap *idmap, struct dentry *dentry,
 LSM_HOOK(void, LSM_RET_VOID, inode_post_setattr, struct mnt_idmap *idmap,
 	 struct dentry *dentry, int ia_valid)
 LSM_HOOK(int, 0, inode_getattr, const struct path *path)
+LSM_HOOK(int, 0, inode_xattr_skipcap, const char *name)
 LSM_HOOK(int, 0, inode_setxattr, struct mnt_idmap *idmap,
 	 struct dentry *dentry, const char *name, const void *value,
 	 size_t size, int flags)
diff --git a/security/security.c b/security/security.c
index e5ca08789f74..8cee5b6c6e6d 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2278,7 +2278,20 @@ int security_inode_getattr(const struct path *path)
  * @size: size of xattr value
  * @flags: flags
  *
- * Check permission before setting the extended attributes.
+ * This hook performs the desired permission checks before setting the extended
+ * attributes (xattrs) on @dentry.  It is important to note that we have some
+ * additional logic before the main LSM implementation calls to detect if we
+ * need to perform an additional capability check at the LSM layer.
+ *
+ * Normally we enforce a capability check prior to executing the various LSM
+ * hook implementations, but if a LSM wants to avoid this capability check,
+ * it can register a 'inode_xattr_skipcap' hook and return a value of 1 for
+ * xattrs that it wants to avoid the capability check, leaving the LSM fully
+ * responsible for enforcing the access control for the specific xattr.  If all
+ * of the enabled LSMs refrain from registering a 'inode_xattr_skipcap' hook,
+ * or return a 0 (the default return value), the capability check is still
+ * performed.  If no 'inode_xattr_skipcap' hooks are registered the capability
+ * check is performed.
  *
  * Return: Returns 0 if permission is granted.
  */
@@ -2286,20 +2299,20 @@ int security_inode_setxattr(struct mnt_idmap *idmap,
 			    struct dentry *dentry, const char *name,
 			    const void *value, size_t size, int flags)
 {
-	int ret;
+	int rc;
 
 	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
 		return 0;
-	/*
-	 * SELinux and Smack integrate the cap call,
-	 * so assume that all LSMs supplying this call do so.
-	 */
-	ret = call_int_hook(inode_setxattr, idmap, dentry, name, value, size,
-			    flags);
 
-	if (ret == 1)
-		ret = cap_inode_setxattr(dentry, name, value, size, flags);
-	return ret;
+	/* enforce the capability checks at the lsm layer, if needed */
+	if (!call_int_hook(inode_xattr_skipcap, name)) {
+		rc = cap_inode_setxattr(dentry, name, value, size, flags);
+		if (rc)
+			return rc;
+	}
+
+	return call_int_hook(inode_setxattr, idmap, dentry, name, value, size,
+			     flags);
 }
 
 /**
@@ -2452,26 +2465,39 @@ int security_inode_listxattr(struct dentry *dentry)
  * @dentry: file
  * @name: xattr name
  *
- * Check permission before removing the extended attribute identified by @name
- * for @dentry.
+ * This hook performs the desired permission checks before setting the extended
+ * attributes (xattrs) on @dentry.  It is important to note that we have some
+ * additional logic before the main LSM implementation calls to detect if we
+ * need to perform an additional capability check at the LSM layer.
+ *
+ * Normally we enforce a capability check prior to executing the various LSM
+ * hook implementations, but if a LSM wants to avoid this capability check,
+ * it can register a 'inode_xattr_skipcap' hook and return a value of 1 for
+ * xattrs that it wants to avoid the capability check, leaving the LSM fully
+ * responsible for enforcing the access control for the specific xattr.  If all
+ * of the enabled LSMs refrain from registering a 'inode_xattr_skipcap' hook,
+ * or return a 0 (the default return value), the capability check is still
+ * performed.  If no 'inode_xattr_skipcap' hooks are registered the capability
+ * check is performed.
  *
  * Return: Returns 0 if permission is granted.
  */
 int security_inode_removexattr(struct mnt_idmap *idmap,
 			       struct dentry *dentry, const char *name)
 {
-	int ret;
+	int rc;
 
 	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
 		return 0;
-	/*
-	 * SELinux and Smack integrate the cap call,
-	 * so assume that all LSMs supplying this call do so.
-	 */
-	ret = call_int_hook(inode_removexattr, idmap, dentry, name);
-	if (ret == 1)
-		ret = cap_inode_removexattr(idmap, dentry, name);
-	return ret;
+
+	/* enforce the capability checks at the lsm layer, if needed */
+	if (!call_int_hook(inode_xattr_skipcap, name)) {
+		rc = cap_inode_removexattr(idmap, dentry, name);
+		if (rc)
+			return rc;
+	}
+
+	return call_int_hook(inode_removexattr, idmap, dentry, name);
 }
 
 /**
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 7eed331e90f0..55c78c318ccd 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3177,6 +3177,23 @@ static bool has_cap_mac_admin(bool audit)
 	return true;
 }
 
+/**
+ * selinux_inode_xattr_skipcap - Skip the xattr capability checks?
+ * @name: name of the xattr
+ *
+ * Returns 1 to indicate that SELinux "owns" the access control rights to xattrs
+ * named @name; the LSM layer should avoid enforcing any traditional
+ * capability based access controls on this xattr.  Returns 0 to indicate that
+ * SELinux does not "own" the access control rights to xattrs named @name and is
+ * deferring to the LSM layer for further access controls, including capability
+ * based controls.
+ */
+static int selinux_inode_xattr_skipcap(const char *name)
+{
+	/* require capability check if not a selinux xattr */
+	return !strcmp(name, XATTR_NAME_SELINUX);
+}
+
 static int selinux_inode_setxattr(struct mnt_idmap *idmap,
 				  struct dentry *dentry, const char *name,
 				  const void *value, size_t size, int flags)
@@ -3188,15 +3205,9 @@ static int selinux_inode_setxattr(struct mnt_idmap *idmap,
 	u32 newsid, sid = current_sid();
 	int rc = 0;
 
-	if (strcmp(name, XATTR_NAME_SELINUX)) {
-		rc = cap_inode_setxattr(dentry, name, value, size, flags);
-		if (rc)
-			return rc;
-
-		/* Not an attribute we recognize, so just check the
-		   ordinary setattr permission. */
+	/* if not a selinux xattr, only check the ordinary setattr perm */
+	if (strcmp(name, XATTR_NAME_SELINUX))
 		return dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
-	}
 
 	if (!selinux_initialized())
 		return (inode_owner_or_capable(idmap, inode) ? 0 : -EPERM);
@@ -3345,15 +3356,9 @@ static int selinux_inode_listxattr(struct dentry *dentry)
 static int selinux_inode_removexattr(struct mnt_idmap *idmap,
 				     struct dentry *dentry, const char *name)
 {
-	if (strcmp(name, XATTR_NAME_SELINUX)) {
-		int rc = cap_inode_removexattr(idmap, dentry, name);
-		if (rc)
-			return rc;
-
-		/* Not an attribute we recognize, so just check the
-		   ordinary setattr permission. */
+	/* if not a selinux xattr, only check the ordinary setattr perm */
+	if (strcmp(name, XATTR_NAME_SELINUX))
 		return dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
-	}
 
 	if (!selinux_initialized())
 		return 0;
@@ -7175,6 +7180,7 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(inode_permission, selinux_inode_permission),
 	LSM_HOOK_INIT(inode_setattr, selinux_inode_setattr),
 	LSM_HOOK_INIT(inode_getattr, selinux_inode_getattr),
+	LSM_HOOK_INIT(inode_xattr_skipcap, selinux_inode_xattr_skipcap),
 	LSM_HOOK_INIT(inode_setxattr, selinux_inode_setxattr),
 	LSM_HOOK_INIT(inode_post_setxattr, selinux_inode_post_setxattr),
 	LSM_HOOK_INIT(inode_getxattr, selinux_inode_getxattr),
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index f5cbec1e6a92..c1fe422cfbe1 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -1283,6 +1283,33 @@ static int smack_inode_getattr(const struct path *path)
 }
 
 /**
+ * smack_inode_xattr_skipcap - Skip the xattr capability checks?
+ * @name: name of the xattr
+ *
+ * Returns 1 to indicate that Smack "owns" the access control rights to xattrs
+ * named @name; the LSM layer should avoid enforcing any traditional
+ * capability based access controls on this xattr.  Returns 0 to indicate that
+ * Smack does not "own" the access control rights to xattrs named @name and is
+ * deferring to the LSM layer for further access controls, including capability
+ * based controls.
+ */
+static int smack_inode_xattr_skipcap(const char *name)
+{
+	if (strncmp(name, XATTR_SMACK_SUFFIX, strlen(XATTR_SMACK_SUFFIX)))
+		return 0;
+
+	if (strcmp(name, XATTR_NAME_SMACK) == 0 ||
+	    strcmp(name, XATTR_NAME_SMACKIPIN) == 0 ||
+	    strcmp(name, XATTR_NAME_SMACKIPOUT) == 0 ||
+	    strcmp(name, XATTR_NAME_SMACKEXEC) == 0 ||
+	    strcmp(name, XATTR_NAME_SMACKMMAP) == 0 ||
+	    strcmp(name, XATTR_NAME_SMACKTRANSMUTE) == 0)
+		return 1;
+
+	return 0;
+}
+
+/**
  * smack_inode_setxattr - Smack check for setting xattrs
  * @idmap: idmap of the mount
  * @dentry: the object
@@ -1325,8 +1352,7 @@ static int smack_inode_setxattr(struct mnt_idmap *idmap,
 		    size != TRANS_TRUE_SIZE ||
 		    strncmp(value, TRANS_TRUE, TRANS_TRUE_SIZE) != 0)
 			rc = -EINVAL;
-	} else
-		rc = cap_inode_setxattr(dentry, name, value, size, flags);
+	}
 
 	if (check_priv && !smack_privileged(CAP_MAC_ADMIN))
 		rc = -EPERM;
@@ -1435,8 +1461,7 @@ static int smack_inode_removexattr(struct mnt_idmap *idmap,
 	    strcmp(name, XATTR_NAME_SMACKMMAP) == 0) {
 		if (!smack_privileged(CAP_MAC_ADMIN))
 			rc = -EPERM;
-	} else
-		rc = cap_inode_removexattr(idmap, dentry, name);
+	}
 
 	if (rc != 0)
 		return rc;
@@ -5053,6 +5078,7 @@ static struct security_hook_list smack_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(inode_permission, smack_inode_permission),
 	LSM_HOOK_INIT(inode_setattr, smack_inode_setattr),
 	LSM_HOOK_INIT(inode_getattr, smack_inode_getattr),
+	LSM_HOOK_INIT(inode_xattr_skipcap, smack_inode_xattr_skipcap),
 	LSM_HOOK_INIT(inode_setxattr, smack_inode_setxattr),
 	LSM_HOOK_INIT(inode_post_setxattr, smack_inode_post_setxattr),
 	LSM_HOOK_INIT(inode_getxattr, smack_inode_getxattr),