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

Roberto Sassu
2023-09-04T13:35:37Z

From: Roberto Sassu <roberto.sassu@huawei.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@huawei.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