[PATCH 1/3] selinux: make dentry_init_security() return security module name

[Casey Schaufler]

On 6/26/2018 1:43 AM, Yan, Zheng wrote:
> This is preparation for CephFS security label. CephFS's implementation uses
> dentry_init_security() to get security context before inode is created,
> then sends open/mkdir/mknod request to MDS, together with security xattr
> "security.<security module name>"

There is no requirement that a security module use
"security.<security module name>" to name it's attributes.
Smack, for example, uses "security.SMACK64". Further, Smack
uses multiple attributes; "security.SMACK64TRANSMUTE",
"security.SMACK64MMAP", "security.SMACK64EXEC" as well as
"security.SMACK64".

Also, when (if) we get full module stacking in place you
will need to handle the possibility that there may be more
than one security module providing security xattrs.

>
> Signed-off-by: "Yan, Zheng" <zyan at redhat.com>
> ---
>  fs/nfs/nfs4proc.c         | 3 ++-
>  include/linux/lsm_hooks.h | 4 ++--
>  include/linux/security.h  | 9 +++++----
>  security/security.c       | 7 ++++---
>  security/selinux/hooks.c  | 8 ++++++--
>  5 files changed, 19 insertions(+), 12 deletions(-)
>
> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> index 6dd146885da9..d18a5fb7aec3 100644
> --- a/fs/nfs/nfs4proc.c
> +++ b/fs/nfs/nfs4proc.c
> @@ -122,7 +122,8 @@ nfs4_label_init_security(struct inode *dir, struct dentry *dentry,
>  		return NULL;
>  
>  	err = security_dentry_init_security(dentry, sattr->ia_mode,
> -				&dentry->d_name, (void **)&label->label, &label->len);
> +				&dentry->d_name,  NULL,
> +				(void **)&label->label, &label->len);
>  	if (err == 0)
>  		return label;
>  
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 8f1131c8dd54..e176c2032bdc 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1476,8 +1476,8 @@ union security_list_options {
>  					unsigned long *set_kern_flags);
>  	int (*sb_parse_opts_str)(char *options, struct security_mnt_opts *opts);
>  	int (*dentry_init_security)(struct dentry *dentry, int mode,
> -					const struct qstr *name, void **ctx,
> -					u32 *ctxlen);
> +					const struct qstr *name, const char **label,
> +					void **ctx, u32 *ctxlen);
>  	int (*dentry_create_files_as)(struct dentry *dentry, int mode,
>  					struct qstr *name,
>  					const struct cred *old,
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 63030c85ee19..df2d73998c64 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -246,8 +246,9 @@ int security_sb_clone_mnt_opts(const struct super_block *oldsb,
>  				unsigned long *set_kern_flags);
>  int security_sb_parse_opts_str(char *options, struct security_mnt_opts *opts);
>  int security_dentry_init_security(struct dentry *dentry, int mode,
> -					const struct qstr *name, void **ctx,
> -					u32 *ctxlen);
> +					const struct qstr *name,
> +					const char **label,
> +					void **ctx, u32 *ctxlen);
>  int security_dentry_create_files_as(struct dentry *dentry, int mode,
>  					struct qstr *name,
>  					const struct cred *old,
> @@ -609,8 +610,8 @@ static inline void security_inode_free(struct inode *inode)
>  static inline int security_dentry_init_security(struct dentry *dentry,
>  						 int mode,
>  						 const struct qstr *name,
> -						 void **ctx,
> -						 u32 *ctxlen)
> +						 const char **label,
> +						 void **ctx, u32 *ctxlen)
>  {
>  	return -EOPNOTSUPP;
>  }
> diff --git a/security/security.c b/security/security.c
> index 68f46d849abe..69818d46aa28 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -450,11 +450,12 @@ void security_inode_free(struct inode *inode)
>  }
>  
>  int security_dentry_init_security(struct dentry *dentry, int mode,
> -					const struct qstr *name, void **ctx,
> -					u32 *ctxlen)
> +					const struct qstr *name,
> +					const char **label,
> +					void **ctx, u32 *ctxlen)
>  {
>  	return call_int_hook(dentry_init_security, -EOPNOTSUPP, dentry, mode,
> -				name, ctx, ctxlen);
> +				name, label, ctx, ctxlen);
>  }
>  EXPORT_SYMBOL(security_dentry_init_security);
>  
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 2b5ee5fbd652..eca3879d9357 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2985,8 +2985,9 @@ static void selinux_inode_free_security(struct inode *inode)
>  }
>  
>  static int selinux_dentry_init_security(struct dentry *dentry, int mode,
> -					const struct qstr *name, void **ctx,
> -					u32 *ctxlen)
> +					const struct qstr *name,
> +					const char **label,
> +					void **ctx, u32 *ctxlen)
>  {
>  	u32 newsid;
>  	int rc;
> @@ -2998,6 +2999,9 @@ static int selinux_dentry_init_security(struct dentry *dentry, int mode,
>  	if (rc)
>  		return rc;
>  
> +	if (label)
> +		*label = XATTR_SELINUX_SUFFIX;
> +
>  	return security_sid_to_context(&selinux_state, newsid, (char **)ctx,
>  				       ctxlen);
>  }

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