linux-kernel - [PATCH v2 02/25] ima: Align ima_post_path_mknod() definition with LSM infrastructure

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Message-Id: <20230831104136.903180-3-roberto.sassu@huaweicloud.com>
Date:   Thu, 31 Aug 2023 12:41:13 +0200
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     viro@...iv.linux.org.uk, brauner@...nel.org,
        chuck.lever@...cle.com, jlayton@...nel.org, neilb@...e.de,
        kolga@...app.com, Dai.Ngo@...cle.com, tom@...pey.com,
        zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
        paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
        dhowells@...hat.com, jarkko@...nel.org,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        casey@...aufler-ca.com
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        selinux@...r.kernel.org, Roberto Sassu <roberto.sassu@...wei.com>
Subject: [PATCH v2 02/25] ima: Align ima_post_path_mknod() definition with LSM infrastructure

From: Roberto Sassu <roberto.sassu@...wei.com>

Change ima_post_path_mknod() definition, so that it can be registered as
implementation of the path_post_mknod hook. Since LSMs see a umask-stripped
mode from security_path_mknod(), pass the same to ima_post_path_mknod() as
well.

Also, make sure that ima_post_path_mknod() is executed only if
(mode & S_IFMT) is equal to zero or S_IFREG.

Add this check to take into account the different placement of the
path_post_mknod hook (to be introduced) in do_mknodat(). Since the new hook
will be placed after the switch(), the check ensures that
ima_post_path_mknod() is invoked as originally intended when it is
registered as implementation of path_post_mknod.

Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
 fs/namei.c                        |  9 ++++++---
 include/linux/ima.h               |  7 +++++--
 security/integrity/ima/ima_main.c | 10 +++++++++-
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index e56ff39a79bc..c5e96f716f98 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4024,6 +4024,7 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode,
 	struct path path;
 	int error;
 	unsigned int lookup_flags = 0;
+	umode_t mode_stripped;
 
 	error = may_mknod(mode);
 	if (error)
@@ -4034,8 +4035,9 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode,
 	if (IS_ERR(dentry))
 		goto out1;
 
-	error = security_path_mknod(&path, dentry,
-			mode_strip_umask(path.dentry->d_inode, mode), dev);
+	mode_stripped = mode_strip_umask(path.dentry->d_inode, mode);
+
+	error = security_path_mknod(&path, dentry, mode_stripped, dev);
 	if (error)
 		goto out2;
 
@@ -4045,7 +4047,8 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode,
 			error = vfs_create(idmap, path.dentry->d_inode,
 					   dentry, mode, true);
 			if (!error)
-				ima_post_path_mknod(idmap, dentry);
+				ima_post_path_mknod(idmap, &path, dentry,
+						    mode_stripped, dev);
 			break;
 		case S_IFCHR: case S_IFBLK:
 			error = vfs_mknod(idmap, path.dentry->d_inode,
diff --git a/include/linux/ima.h b/include/linux/ima.h
index 910a2f11a906..179ce52013b2 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -32,7 +32,8 @@ extern int ima_read_file(struct file *file, enum kernel_read_file_id id,
 extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
 			      enum kernel_read_file_id id);
 extern void ima_post_path_mknod(struct mnt_idmap *idmap,
-				struct dentry *dentry);
+				const struct path *dir, struct dentry *dentry,
+				umode_t mode, unsigned int dev);
 extern int ima_file_hash(struct file *file, char *buf, size_t buf_size);
 extern int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size);
 extern void ima_kexec_cmdline(int kernel_fd, const void *buf, int size);
@@ -114,7 +115,9 @@ static inline int ima_post_read_file(struct file *file, void *buf, loff_t size,
 }
 
 static inline void ima_post_path_mknod(struct mnt_idmap *idmap,
-				       struct dentry *dentry)
+				       const struct path *dir,
+				       struct dentry *dentry,
+				       umode_t mode, unsigned int dev)
 {
 	return;
 }
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 365db0e43d7c..76eba92d7f10 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -696,18 +696,26 @@ void ima_post_create_tmpfile(struct mnt_idmap *idmap,
 /**
  * ima_post_path_mknod - mark as a new inode
  * @idmap: idmap of the mount the inode was found from
+ * @dir: path structure of parent of the new file
  * @dentry: newly created dentry
+ * @mode: mode of the new file
+ * @dev: undecoded device number
  *
  * Mark files created via the mknodat syscall as new, so that the
  * file data can be written later.
  */
 void ima_post_path_mknod(struct mnt_idmap *idmap,
-			 struct dentry *dentry)
+			 const struct path *dir, struct dentry *dentry,
+			 umode_t mode, unsigned int dev)
 {
 	struct integrity_iint_cache *iint;
 	struct inode *inode = dentry->d_inode;
 	int must_appraise;
 
+	/* See do_mknodat(), IMA is executed for case 0: and case S_IFREG: */
+	if ((mode & S_IFMT) != 0 && (mode & S_IFMT) != S_IFREG)
+		return;
+
 	if (!ima_policy_flag || !S_ISREG(inode->i_mode))
 		return;
 
-- 
2.34.1