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

[Stefan Berger]

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>