[PATCH 7/7] smack: Don't use security labels for user namespace mounts

Seth Forshee
2015-07-15T19:47:31Z

Avoid use of untrusted security labels when s_user_ns !=
init_user_ns:
- smk_fetch: refuse to read labels from disk
- smack_inode_init_security: return -ENOTSUPP
- smack_d_instantiate: don't use security xattrs from disk

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
security/smack/smack_lsm.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index a143328f75eb..6a849da94f47 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -255,6 +255,9 @@ static struct smack_known *smk_fetch(const char *name, struct inode *ip,
char *buffer;
struct smack_known *skp = NULL;

+ if (ip->i_sb->s_user_ns != &init_user_ns)
+ return NULL;
+
if (ip->i_op->getxattr == NULL)
return ERR_PTR(-EOPNOTSUPP);

@@ -833,6 +836,9 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
struct smack_known *dsp = smk_of_inode(dir);
int may;

+ if (inode->i_sb->s_user_ns != &init_user_ns)
+ return -ENOTSUPP;
+
if (name)
*name = XATTR_SMACK_SUFFIX;

@@ -3176,11 +3182,13 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
}
/*
* No xattr support means, alas, no SMACK label.
- * Use the aforeapplied default.
+ * Use the aforeapplied default. Also don't use
+ * xattrs from userns mounts.
* It would be curious if the label of the task
* does not match that assigned.
*/
- if (inode->i_op->getxattr == NULL)
+ if (inode->i_sb->s_user_ns != &init_user_ns ||
+ inode->i_op->getxattr == NULL)
break;
/*
* Get the dentry for xattr.
--
1.9.1