Wire up security_inode_mknod_capns() in fs/namei.c. If implemented
and access is granted by an lsm, check ns_capable() instead of the
global CAP_MKNOD.
Wire up security_sb_alloc_userns() in fs/super.c. If implemented
and access is granted by an lsm, the created super block will allow
access to device nodes also if it was created in a non-inital userns.
Signed-off-by: Michael Weiß <michael.weiss@xxxxxxxxxxxxxxxxxxx>
---
fs/namei.c | 16 +++++++++++++++-
fs/super.c | 6 +++++-
2 files changed, 20 insertions(+), 2 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index f601fcbdc4d2..1f68d160e2c0 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3949,6 +3949,20 @@ inline struct dentry *user_path_create(int dfd, const char __user *pathname,
}
EXPORT_SYMBOL(user_path_create);
+static bool mknod_capable(struct inode *dir, struct dentry *dentry,
+ umode_t mode, dev_t dev)
+{
+ /*
+ * In case of a security hook implementation check mknod in user
+ * namespace. Otherwise just check global capability.
+ */
+ int error = security_inode_mknod_nscap(dir, dentry, mode, dev);
+ if (!error)
+ return ns_capable(current_user_ns(), CAP_MKNOD);
+ else
+ return capable(CAP_MKNOD);
+}
+
/**
* vfs_mknod - create device node or file
* @idmap: idmap of the mount the inode was found from
@@ -3975,7 +3989,7 @@ int vfs_mknod(struct mnt_idmap *idmap, struct inode *dir,
return error;
if ((S_ISCHR(mode) || S_ISBLK(mode)) && !is_whiteout &&
- !capable(CAP_MKNOD))
+ !mknod_capable(dir, dentry, mode, dev))
return -EPERM;
if (!dir->i_op->mknod)
diff --git a/fs/super.c b/fs/super.c
index 2d762ce67f6e..bb01db6d9986 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -362,7 +362,11 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
}
s->s_bdi = &noop_backing_dev_info;
s->s_flags = flags;
- if (s->s_user_ns != &init_user_ns)
+ /*
+ * We still have to think about this here. Several concerns exist
+ * about the security model, especially about malicious fuse.
+ */
+ if (s->s_user_ns != &init_user_ns && security_sb_alloc_userns(s))
s->s_iflags |= SB_I_NODEV;
INIT_HLIST_NODE(&s->s_instances);
INIT_HLIST_BL_HEAD(&s->s_roots);
--
2.30.2
