On 1/24/20 1:42 PM, Christian Göttsche wrote:
Currently symlinks on kernel filesystems, like sysfs, are labeled on
creation with the parent fs 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: kernfs_sovereign_symlinks
Signed-off-by: Christian Göttsche <cgzones@xxxxxxxxxxxxxx>
---
security/selinux/hooks.c | 5 ++++-
security/selinux/include/security.h | 8 ++++++++
security/selinux/ss/services.c | 3 ++-
3 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index d9e8b2131..1303bc8c4 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1475,7 +1475,10 @@ 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_kernfs_sovereign_symlinks() &&
Not fond of the name. 1) kernfs is a kernel implementation detail,
shouldn't be exposed to policy; genfs is the policy construct 2)
sovereign doesn't seem to fit the meaning of this capability; seclabel
would be more appropriate.
+ (sbsec->flags & SE_SBGENFS_XATTR))) {
Why limit this to SE_SBGENFS_XATTR filesystems? Why not just make the test:
if ((sbsec->flags & SE_SBGENFS) && (!S_ISLNK(inode->i_mode) ||
selinux_policycap_genfs_symlinkseclabel()))
or similar.
/* 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 a39f9565d..cc8217848 100644
--- 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_KERNFS_SOVEREIGN_SYMLINKS,
__POLICYDB_CAPABILITY_MAX
};
#define POLICYDB_CAPABILITY_MAX (__POLICYDB_CAPABILITY_MAX - 1)
@@ -209,6 +210,13 @@ static inline bool selinux_policycap_nnp_nosuid_transition(void)
return state->policycap[POLICYDB_CAPABILITY_NNP_NOSUID_TRANSITION];
}
+static inline bool selinux_policycap_kernfs_sovereign_symlinks(void)
+{
+ struct selinux_state *state = &selinux_state;
+
+ return state->policycap[POLICYDB_CAPABILITY_KERNFS_SOVEREIGN_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 216ce602a..b70380947 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -73,7 +73,8 @@ const char *selinux_policycap_names[__POLICYDB_CAPABILITY_MAX] = {
"extended_socket_class",
"always_check_network",
"cgroup_seclabel",
- "nnp_nosuid_transition"
+ "nnp_nosuid_transition",
+ "kernfs_sovereign_symlinks"
};
static struct selinux_ss selinux_ss;
