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

[Roberto Sassu]

On Wed, 2023-10-11 at 10:38 -0400, Mimi Zohar wrote:
> On Mon, 2023-09-04 at 15:33 +0200, 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().
> 
> 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@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;
> > +
> 
> There's already a check below to make sure that this is a regular file.
> Are both needed?

You are right, I can remove the first check.

Thanks

Roberto

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