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

Mimi Zohar
2023-10-11T14:39:06Z

On Mon, 2023-09-04 at 15:33 +0200, Roberto Sassu wrote:
> 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().

Move "(to be introduced)" to when it is first mentioned.

> 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;
> +

There's already a check below to make sure that this is a regular file.
Are both needed?

> if (!ima_policy_flag || !S_ISREG(inode->i_mode))
> return;
>