selinux: allow kernfs symlinks to inherit parent directory context

Currently symlinks on kernel filesystems, like sysfs, are labeled on
creation with the parent filesystem root sid.

Allow symlinks to inherit the parent directory context, so fine-grained
kernfs labeling can be applied to symlinks too and checking contexts
doesn't complain about them.

For backward-compatibility this behavior is contained in a new policy
capability: genfs_seclabel_symlinks

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Acked-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 d776226..7c37cdb 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1478,7 +1478,9 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
                /* Default to the fs superblock SID. */
                sid = sbsec->sid;
 
-               if ((sbsec->flags & SE_SBGENFS) && !S_ISLNK(inode->i_mode)) {
+               if ((sbsec->flags & SE_SBGENFS) &&
+                    (!S_ISLNK(inode->i_mode) ||
+                     selinux_policycap_genfs_seclabel_symlinks())) {
                        /* We must have a dentry to determine the label on
                         * procfs inodes */
                        if (opt_dentry) {

diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index f3a6210..d6036c0 100644 (file)
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -79,6 +79,7 @@ enum {
        POLICYDB_CAPABILITY_ALWAYSNETWORK,
        POLICYDB_CAPABILITY_CGROUPSECLABEL,
        POLICYDB_CAPABILITY_NNP_NOSUID_TRANSITION,
+       POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS,
        __POLICYDB_CAPABILITY_MAX
 };
 #define POLICYDB_CAPABILITY_MAX (__POLICYDB_CAPABILITY_MAX - 1)
@@ -213,6 +214,13 @@ static inline bool selinux_policycap_nnp_nosuid_transition(void)
        return state->policycap[POLICYDB_CAPABILITY_NNP_NOSUID_TRANSITION];
 }
 
+static inline bool selinux_policycap_genfs_seclabel_symlinks(void)
+{
+       struct selinux_state *state = &selinux_state;
+
+       return state->policycap[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS];
+}
+
 int security_mls_enabled(struct selinux_state *state);
 int security_load_policy(struct selinux_state *state,
                         void *data, size_t len);

diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 922b5e4..e310f8e 100644 (file)
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -72,7 +72,8 @@ const char *selinux_policycap_names[__POLICYDB_CAPABILITY_MAX] = {
        "extended_socket_class",
        "always_check_network",
        "cgroup_seclabel",
-       "nnp_nosuid_transition"
+       "nnp_nosuid_transition",
+       "genfs_seclabel_symlinks"
 };
 
 static struct selinux_ss selinux_ss;