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Commit d07b846f authored by Seth Forshee's avatar Seth Forshee Committed by Eric W. Biederman
Browse files

fs: Limit file caps to the user namespace of the super block 



Capability sets attached to files must be ignored except in the
user namespaces where the mounter is privileged, i.e. s_user_ns
and its descendants. Otherwise a vector exists for gaining
privileges in namespaces where a user is not already privileged.

Add a new helper function, current_in_user_ns(), to test whether a user
namespace is the same as or a descendant of another namespace.
Use this helper to determine whether a file's capability set
should be applied to the caps constructed during exec.

--EWB Replaced in_userns with the simpler current_in_userns.

Acked-by: default avatarSerge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: default avatarSeth Forshee <seth.forshee@canonical.com>
Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
parent cc50a07a

include/linux/user_namespace.h

+6 −0
Original line number Diff line number Diff line
@@ -72,6 +72,7 @@ extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, 
extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t, loff_t *);

extern int proc_setgroups_show(struct seq_file *m, void *v);

extern bool userns_may_setgroups(const struct user_namespace *ns);

extern bool current_in_userns(const struct user_namespace *target_ns);

#else



static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
@@ -100,6 +101,11 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns) 
{

	return true;

}



static inline bool current_in_userns(const struct user_namespace *target_ns)

{

	return true;

}

#endif



#endif /* _LINUX_USER_H */

kernel/user_namespace.c

+14 −0
Original line number Diff line number Diff line
@@ -938,6 +938,20 @@ bool userns_may_setgroups(const struct user_namespace *ns) 
	return allowed;

}



/*

 * Returns true if @ns is the same namespace as or a descendant of

 * @target_ns.

 */

bool current_in_userns(const struct user_namespace *target_ns)

{

	struct user_namespace *ns;

	for (ns = current_user_ns(); ns; ns = ns->parent) {

		if (ns == target_ns)

			return true;

	}

	return false;

}



static inline struct user_namespace *to_user_ns(struct ns_common *ns)

{

	return container_of(ns, struct user_namespace, ns);

security/commoncap.c

+2 −0
Original line number Diff line number Diff line
@@ -455,6 +455,8 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c 


	if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)

		return 0;

	if (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns))

		return 0;



	rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);

	if (rc < 0) {