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>
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 9926adb..9cc042d 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -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,
