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

[Stephen Smalley]

On 06/26/2018 04:43 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>"

Can you describe how your approach compares to the NFSv4 labeling support, and why it requires
exporting this information from this hook when NFSv4 did not?

> 
> 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,

Seems like "label" could be confusing given that it means something else in the NFSv4 code,
and what is actually being provided here is the xattr name suffix.

> +					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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