Re: [PATCH v3 02/25] ima: Align ima_post_path_mknod() definition with LSM infrastructure

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On 9/4/23 09:33, Roberto Sassu wrote:

From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>

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@xxxxxxxxxx>
---
  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;
+

These checks are only needed later (16/25) but IMO ok to introduce now.

Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>





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