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Commit 0b4d3452 authored by Scott Mayhew's avatar Scott Mayhew Committed by Paul Moore
Browse files

security/selinux: allow security_sb_clone_mnt_opts to enable/disable native labeling behavior 

When an NFSv4 client performs a mount operation, it first mounts the
NFSv4 root and then does path walk to the exported path and performs a
submount on that, cloning the security mount options from the root's
superblock to the submount's superblock in the process.

Unless the NFS server has an explicit fsid=0 export with the
"security_label" option, the NFSv4 root superblock will not have
SBLABEL_MNT set, and neither will the submount superblock after cloning
the security mount options.  As a result, setxattr's of security labels
over NFSv4.2 will fail.  In a similar fashion, NFSv4.2 mounts mounted
with the context= mount option will not show the correct labels because
the nfs_server->caps flags of the cloned superblock will still have
NFS_CAP_SECURITY_LABEL set.

Allowing the NFSv4 client to enable or disable SECURITY_LSM_NATIVE_LABELS
behavior will ensure that the SBLABEL_MNT flag has the correct value
when the client traverses from an exported path without the
"security_label" option to one with the "security_label" option and
vice versa.  Similarly, checking to see if SECURITY_LSM_NATIVE_LABELS is
set upon return from security_sb_clone_mnt_opts() and clearing
NFS_CAP_SECURITY_LABEL if necessary will allow the correct labels to
be displayed for NFSv4.2 mounts mounted with the context= mount option.

Resolves: https://github.com/SELinuxProject/selinux-kernel/issues/35



Signed-off-by: default avatarScott Mayhew <smayhew@redhat.com>
Reviewed-by: default avatarStephen Smalley <sds@tycho.nsa.gov>
Tested-by: default avatarStephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: default avatarPaul Moore <paul@paul-moore.com>
parent b4958c89

fs/nfs/super.c

+16 −1
Original line number Diff line number Diff line
@@ -2544,10 +2544,25 @@ EXPORT_SYMBOL_GPL(nfs_set_sb_security); 
int nfs_clone_sb_security(struct super_block *s, struct dentry *mntroot,

			  struct nfs_mount_info *mount_info)

{

	int error;

	unsigned long kflags = 0, kflags_out = 0;



	/* clone any lsm security options from the parent to the new sb */

	if (d_inode(mntroot)->i_op != NFS_SB(s)->nfs_client->rpc_ops->dir_inode_ops)

		return -ESTALE;

	return security_sb_clone_mnt_opts(mount_info->cloned->sb, s);



	if (NFS_SB(s)->caps & NFS_CAP_SECURITY_LABEL)

		kflags |= SECURITY_LSM_NATIVE_LABELS;



	error = security_sb_clone_mnt_opts(mount_info->cloned->sb, s, kflags,

			&kflags_out);

	if (error)

		return error;



	if (NFS_SB(s)->caps & NFS_CAP_SECURITY_LABEL &&

		!(kflags_out & SECURITY_LSM_NATIVE_LABELS))

		NFS_SB(s)->caps &= ~NFS_CAP_SECURITY_LABEL;

	return 0;

}

EXPORT_SYMBOL_GPL(nfs_clone_sb_security);

include/linux/lsm_hooks.h

+3 −1
Original line number Diff line number Diff line
@@ -1409,7 +1409,9 @@ union security_list_options { 
				unsigned long kern_flags,

				unsigned long *set_kern_flags);

	int (*sb_clone_mnt_opts)(const struct super_block *oldsb,

					struct super_block *newsb);

					struct super_block *newsb,

					unsigned long kern_flags,

					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,

include/linux/security.h

+6 −2
Original line number Diff line number Diff line
@@ -249,7 +249,9 @@ int security_sb_set_mnt_opts(struct super_block *sb, 
				unsigned long kern_flags,

				unsigned long *set_kern_flags);

int security_sb_clone_mnt_opts(const struct super_block *oldsb,

				struct super_block *newsb);

				struct super_block *newsb,

				unsigned long kern_flags,

				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,
@@ -605,7 +607,9 @@ static inline int security_sb_set_mnt_opts(struct super_block *sb, 
}



static inline int security_sb_clone_mnt_opts(const struct super_block *oldsb,

					      struct super_block *newsb)

					      struct super_block *newsb,

					      unsigned long kern_flags,

					      unsigned long *set_kern_flags)

{

	return 0;

}

security/security.c

+5 −2
Original line number Diff line number Diff line
@@ -420,9 +420,12 @@ int security_sb_set_mnt_opts(struct super_block *sb, 
EXPORT_SYMBOL(security_sb_set_mnt_opts);



int security_sb_clone_mnt_opts(const struct super_block *oldsb,

				struct super_block *newsb)

				struct super_block *newsb,

				unsigned long kern_flags,

				unsigned long *set_kern_flags)

{

	return call_int_hook(sb_clone_mnt_opts, 0, oldsb, newsb);

	return call_int_hook(sb_clone_mnt_opts, 0, oldsb, newsb,

				kern_flags, set_kern_flags);

}

EXPORT_SYMBOL(security_sb_clone_mnt_opts);

security/selinux/hooks.c

+33 −2
Original line number Diff line number Diff line
@@ -525,8 +525,16 @@ static int sb_finish_set_opts(struct super_block *sb) 
	}



	sbsec->flags |= SE_SBINITIALIZED;



	/*

	 * Explicitly set or clear SBLABEL_MNT.  It's not sufficient to simply

	 * leave the flag untouched because sb_clone_mnt_opts might be handing

	 * us a superblock that needs the flag to be cleared.

	 */

	if (selinux_is_sblabel_mnt(sb))

		sbsec->flags |= SBLABEL_MNT;

	else

		sbsec->flags &= ~SBLABEL_MNT;



	/* Initialize the root inode. */

	rc = inode_doinit_with_dentry(root_inode, root);
@@ -959,8 +967,11 @@ static int selinux_cmp_sb_context(const struct super_block *oldsb, 
}



static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb,

					struct super_block *newsb)

					struct super_block *newsb,

					unsigned long kern_flags,

					unsigned long *set_kern_flags)

{

	int rc = 0;

	const struct superblock_security_struct *oldsbsec = oldsb->s_security;

	struct superblock_security_struct *newsbsec = newsb->s_security;
@@ -975,6 +986,13 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb, 
	if (!ss_initialized)

		return 0;



	/*

	 * Specifying internal flags without providing a place to

	 * place the results is not allowed.

	 */

	if (kern_flags && !set_kern_flags)

		return -EINVAL;



	/* how can we clone if the old one wasn't set up?? */

	BUG_ON(!(oldsbsec->flags & SE_SBINITIALIZED));
@@ -990,6 +1008,18 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb, 
	newsbsec->def_sid = oldsbsec->def_sid;

	newsbsec->behavior = oldsbsec->behavior;



	if (newsbsec->behavior == SECURITY_FS_USE_NATIVE &&

		!(kern_flags & SECURITY_LSM_NATIVE_LABELS) && !set_context) {

		rc = security_fs_use(newsb);

		if (rc)

			goto out;

	}



	if (kern_flags & SECURITY_LSM_NATIVE_LABELS && !set_context) {

		newsbsec->behavior = SECURITY_FS_USE_NATIVE;

		*set_kern_flags |= SECURITY_LSM_NATIVE_LABELS;

	}



	if (set_context) {

		u32 sid = oldsbsec->mntpoint_sid;
@@ -1009,8 +1039,9 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb, 
	}



	sb_finish_set_opts(newsb);

out:

	mutex_unlock(&newsbsec->lock);

	return 0;

	return rc;

}



static int selinux_parse_opts_str(char *options,