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: Scott Mayhew <smayhew@redhat.com>
Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
Tested-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/include/linux/security.h b/include/linux/security.h
index 549cb828a888..b44e954815ce 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -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;
 }