[PATCH v7 7/7] fuse: Restrict allow_other to the superblock's namespace or a descendant

Eric W. Biederman ebiederm at xmission.com
Mon Feb 26 23:53:02 UTC 2018


From: Seth Forshee <seth.forshee at canonical.com>

Unprivileged users are normally restricted from mounting with the
allow_other option by system policy, but this could be bypassed
for a mount done with user namespace root permissions. In such
cases allow_other should not allow users outside the userns
to access the mount as doing so would give the unprivileged user
the ability to manipulate processes it would otherwise be unable
to manipulate. Restrict allow_other to apply to users in the same
userns used at mount or a descendant of that namespace. Also
export current_in_userns() for use by fuse when built as a
module.

Cc: linux-fsdevel at vger.kernel.org
Cc: linux-kernel at vger.kernel.org
Cc: "Eric W. Biederman" <ebiederm at xmission.com>
Cc: Serge Hallyn <serge at hallyn.com>
Cc: Miklos Szeredi <mszeredi at redhat.com>
Acked-by: Miklos Szeredi <mszeredi at redhat.com>
Reviewed-by: Serge Hallyn <serge at hallyn.com>
Reviewed-by: "Eric W. Biederman" <ebiederm at xmission.com>
Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
Signed-off-by: Dongsu Park <dongsu at kinvolk.io>
Signed-off-by: Eric W. Biederman <ebiederm at xmission.com>
---
 fs/fuse/dir.c           | 2 +-
 kernel/user_namespace.c | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 79cca1687457..0cbd1ff3dd48 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1030,7 +1030,7 @@ int fuse_allow_current_process(struct fuse_conn *fc)
 	const struct cred *cred;
 
 	if (fc->allow_other)
-		return 1;
+		return current_in_userns(fc->user_ns);
 
 	cred = current_cred();
 	if (uid_eq(cred->euid, fc->user_id) &&
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 246d4d4ce5c7..492c255e6c5a 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -1235,6 +1235,7 @@ bool current_in_userns(const struct user_namespace *target_ns)
 {
 	return in_userns(target_ns, current_user_ns());
 }
+EXPORT_SYMBOL(current_in_userns);
 
 static inline struct user_namespace *to_user_ns(struct ns_common *ns)
 {
-- 
2.14.1



More information about the Containers mailing list