Re: [PATCH 01/13] Security: Add hook to calculate context based on a negative dentry.

["J. Bruce Fields" <bfields@fieldses.org>]

On Mon, Nov 12, 2012 at 01:15:35AM -0500, David Quigley wrote:
> From: David Quigley <dpquigl@davequigley.com>
> 
> There is a time where we need to calculate a context without the
> inode having been created yet. To do this we take the negative dentry and
> calculate a context based on the process and the parent directory contexts.
> 
> Signed-off-by: Matthew N. Dodd <Matthew.Dodd@sparta.com>
> Signed-off-by: Miguel Rodel Felipe <Rodel_FM@dsi.a-star.edu.sg>
> Signed-off-by: Phua Eu Gene <PHUA_Eu_Gene@dsi.a-star.edu.sg>
> Signed-off-by: Khin Mi Mi Aung <Mi_Mi_AUNG@dsi.a-star.edu.sg>
> Signed-off-by: David Quigley <dpquigl@davequigley.com>
> ---
>  include/linux/security.h | 27 +++++++++++++++++++++++++++
>  security/capability.c    |  8 ++++++++
>  security/security.c      | 10 ++++++++++
>  security/selinux/hooks.c | 35 +++++++++++++++++++++++++++++++++++
>  4 files changed, 80 insertions(+)
> 
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 05e88bd..c9f5eec 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -26,6 +26,7 @@
>  #include <linux/capability.h>
>  #include <linux/slab.h>
>  #include <linux/err.h>
> +#include <linux/string.h>
>  
>  struct linux_binprm;
>  struct cred;
> @@ -306,6 +307,15 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
>   *	Parse a string of security data filling in the opts structure
>   *	@options string containing all mount options known by the LSM
>   *	@opts binary data structure usable by the LSM
> + * @dentry_init_security:
> + *	Compute a context for a dentry as the inode is not yet available
> + *	since NFSv4 has no label backed by an EA anyway.

I don't understand this comment.  Why exactly is NFSv4 the first user
that needs this?

--b.

> + *	@dentry dentry to use in calculating the context.
> + *	@mode mode used to determine resource type.
> + *	@name name of the last path component used to create file
> + *	@ctx pointer to place the pointer to the resulting context in.
> + *	@ctxlen point to place the length of the resulting context.
> + *
>   *
>   * Security hooks for inode operations.
>   *
> @@ -1421,6 +1431,10 @@ struct security_operations {
>  	void (*sb_clone_mnt_opts) (const struct super_block *oldsb,
>  				   struct super_block *newsb);
>  	int (*sb_parse_opts_str) (char *options, struct security_mnt_opts *opts);
> +	int (*dentry_init_security) (struct dentry *dentry, int mode,
> +					struct qstr *name, void **ctx,
> +					u32 *ctxlen);
> +
>  
>  #ifdef CONFIG_SECURITY_PATH
>  	int (*path_unlink) (struct path *dir, struct dentry *dentry);
> @@ -1702,6 +1716,9 @@ int security_sb_set_mnt_opts(struct super_block *sb, struct security_mnt_opts *o
>  void security_sb_clone_mnt_opts(const struct super_block *oldsb,
>  				struct super_block *newsb);
>  int security_sb_parse_opts_str(char *options, struct security_mnt_opts *opts);
> +int security_dentry_init_security(struct dentry *dentry, int mode,
> +					struct qstr *name, void **ctx,
> +					u32 *ctxlen);
>  
>  int security_inode_alloc(struct inode *inode);
>  void security_inode_free(struct inode *inode);
> @@ -2005,6 +2022,16 @@ static inline int security_inode_alloc(struct inode *inode)
>  static inline void security_inode_free(struct inode *inode)
>  { }
>  
> +static inline int security_dentry_init_security(struct dentry *dentry,
> +						 int mode,
> +						 struct qstr *name,
> +						 void **ctx,
> +						 u32 *ctxlen)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +
>  static inline int security_inode_init_security(struct inode *inode,
>  						struct inode *dir,
>  						const struct qstr *qstr,
> diff --git a/security/capability.c b/security/capability.c
> index b14a30c..f1eb284 100644
> --- a/security/capability.c
> +++ b/security/capability.c
> @@ -108,6 +108,13 @@ static int cap_sb_parse_opts_str(char *options, struct security_mnt_opts *opts)
>  	return 0;
>  }
>  
> +static int cap_dentry_init_security(struct dentry *dentry, int mode,
> +					struct qstr *name, void **ctx,
> +					u32 *ctxlen)
> +{
> +	return 0;
> +}
> +
>  static int cap_inode_alloc_security(struct inode *inode)
>  {
>  	return 0;
> @@ -905,6 +912,7 @@ void __init security_fixup_ops(struct security_operations *ops)
>  	set_to_cap_if_null(ops, sb_set_mnt_opts);
>  	set_to_cap_if_null(ops, sb_clone_mnt_opts);
>  	set_to_cap_if_null(ops, sb_parse_opts_str);
> +	set_to_cap_if_null(ops, dentry_init_security);
>  	set_to_cap_if_null(ops, inode_alloc_security);
>  	set_to_cap_if_null(ops, inode_free_security);
>  	set_to_cap_if_null(ops, inode_init_security);
> diff --git a/security/security.c b/security/security.c
> index 8dcd4ae..b4b2017 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -12,6 +12,7 @@
>   */
>  
>  #include <linux/capability.h>
> +#include <linux/dcache.h>
>  #include <linux/module.h>
>  #include <linux/init.h>
>  #include <linux/kernel.h>
> @@ -324,6 +325,15 @@ void security_inode_free(struct inode *inode)
>  	security_ops->inode_free_security(inode);
>  }
>  
> +int security_dentry_init_security(struct dentry *dentry, int mode,
> +					struct qstr *name, void **ctx,
> +					u32 *ctxlen)
> +{
> +	return security_ops->dentry_init_security(dentry, mode, name,
> +							ctx, ctxlen);
> +}
> +EXPORT_SYMBOL(security_dentry_init_security);
> +
>  int security_inode_init_security(struct inode *inode, struct inode *dir,
>  				 const struct qstr *qstr,
>  				 const initxattrs initxattrs, void *fs_data)
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 61a5336..22d9adf 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2483,6 +2483,40 @@ static void selinux_inode_free_security(struct inode *inode)
>  	inode_free_security(inode);
>  }
>  
> +static int selinux_dentry_init_security(struct dentry *dentry, int mode,
> +					struct qstr *name, void **ctx,
> +					u32 *ctxlen)
> +{
> +	struct cred *cred = current_cred();
> +	struct task_security_struct *tsec;
> +	struct inode_security_struct *dsec;
> +	struct superblock_security_struct *sbsec;
> +	struct inode *dir = dentry->d_parent->d_inode;
> +	u32 newsid;
> +	int rc;
> +
> +	tsec = cred->security;
> +	dsec = dir->i_security;
> +	sbsec = dir->i_sb->s_security;
> +
> +	if (tsec->create_sid && sbsec->behavior != SECURITY_FS_USE_MNTPOINT) {
> +		newsid = tsec->create_sid;
> +	} else {
> +		rc = security_transition_sid(tsec->sid, dsec->sid,
> +					     inode_mode_to_security_class(mode),
> +					     name,
> +					     &newsid);
> +		if (rc) {
> +			printk(KERN_WARNING
> +				"%s: security_transition_sid failed, rc=%d\n",
> +			       __func__, -rc);
> +			return rc;
> +		}
> +	}
> +
> +	return security_sid_to_context(newsid, (char **)ctx, ctxlen);
> +}
> +
>  static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
>  				       const struct qstr *qstr, char **name,
>  				       void **value, size_t *len)
> @@ -5509,6 +5543,7 @@ static struct security_operations selinux_ops = {
>  	.sb_clone_mnt_opts =		selinux_sb_clone_mnt_opts,
>  	.sb_parse_opts_str = 		selinux_parse_opts_str,
>  
> +	.dentry_init_security =		selinux_dentry_init_security,
>  
>  	.inode_alloc_security =		selinux_inode_alloc_security,
>  	.inode_free_security =		selinux_inode_free_security,
> -- 
> 1.7.11.7
>