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From: Casey Schaufler <casey@schaufler-ca.com>
To: casey@schaufler-ca.com,
	paul@paul-moore.com,
	linux-security-module@vger.kernel.org
Cc: jmorris@namei.org,
	serge@hallyn.com,
	keescook@chromium.org,
	john.johansen@canonical.com,
	penguin-kernel@i-love.sakura.ne.jp,
	stephen.smalley.work@gmail.com,
	linux-kernel@vger.kernel.org,
	mic@digikod.net
Subject: [PATCH v39 38/42] LSM: Correct handling of ENOSYS in inode_setxattr
Date: Fri, 15 Dec 2023 14:16:32 -0800
Message-ID: <20231215221636.105680-39-casey@schaufler-ca.com>
In-Reply-To: <20231215221636.105680-1-casey@schaufler-ca.com>
References: <20231215221636.105680-1-casey@schaufler-ca.com>
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The usual "bail on fail" behavior of LSM hooks doesn't
work for security_inode_setxattr(). Modules are allowed
to return -ENOSYS if the attribute specified isn't one
they manage. Fix the code to accommodate this unusal case.
This requires changes to the hooks in SELinux and Smack.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
 security/security.c        | 29 +++++++++++++++--------------
 security/selinux/hooks.c   |  7 ++-----
 security/smack/smack_lsm.c | 10 +++++-----
 3 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/security/security.c b/security/security.c
index 64cdf0e09832..b1a849e8589c 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2346,24 +2346,25 @@ int security_inode_setxattr(struct mnt_idmap *idmap,
 			    struct dentry *dentry, const char *name,
 			    const void *value, size_t size, int flags)
 {
-	int ret;
+	struct security_hook_list *hp;
+	int rc = -ENOSYS;
 
 	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, 1, idmap, dentry, name, value,
-			    size, flags);
 
-	if (ret == 1)
-		ret = cap_inode_setxattr(dentry, name, value, size, flags);
-	if (ret)
-		return ret;
-	ret = ima_inode_setxattr(dentry, name, value, size);
-	if (ret)
-		return ret;
+	hlist_for_each_entry(hp, &security_hook_heads.inode_setxattr, list) {
+		rc = hp->hook.inode_setxattr(idmap, dentry, name, value, size,
+					     flags);
+		if (rc != -ENOSYS)
+			break;
+	}
+	if (rc == -ENOSYS)
+		rc = cap_inode_setxattr(dentry, name, value, size, flags);
+	if (rc)
+		return rc;
+	rc = ima_inode_setxattr(dentry, name, value, size);
+	if (rc)
+		return rc;
 	return evm_inode_setxattr(idmap, dentry, name, value, size);
 }
 
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 46dee63eec12..4ac4b536c568 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3207,13 +3207,10 @@ static int selinux_inode_setxattr(struct mnt_idmap *idmap,
 	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. */
-		return dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
+		rc = dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
+		return rc ? rc : -ENOSYS;
 	}
 
 	if (!selinux_initialized())
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 61bd3f626e7d..02b9aa200ad4 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -1340,7 +1340,7 @@ static int smack_inode_setxattr(struct mnt_idmap *idmap,
 		    strncmp(value, TRANS_TRUE, TRANS_TRUE_SIZE) != 0)
 			rc = -EINVAL;
 	} else
-		rc = cap_inode_setxattr(dentry, name, value, size, flags);
+		rc = -ENOSYS;
 
 	if (check_priv && !smack_privileged(CAP_MAC_ADMIN))
 		rc = -EPERM;
@@ -1354,11 +1354,11 @@ static int smack_inode_setxattr(struct mnt_idmap *idmap,
 			rc = -EINVAL;
 	}
 
-	smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_DENTRY);
-	smk_ad_setfield_u_fs_path_dentry(&ad, dentry);
-
 	if (rc == 0) {
-		rc = smk_curacc(smk_of_inode(d_backing_inode(dentry)), MAY_WRITE, &ad);
+		smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_DENTRY);
+		smk_ad_setfield_u_fs_path_dentry(&ad, dentry);
+		rc = smk_curacc(smk_of_inode(d_backing_inode(dentry)),
+				MAY_WRITE, &ad);
 		rc = smk_bu_inode(d_backing_inode(dentry), MAY_WRITE, rc);
 	}
 
-- 
2.41.0