| Message ID | 1443039368-55445-5-git-send-email-seth.forshee@canonical.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Seth Forshee <seth.forshee@canonical.com> writes: > 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, 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. No issues with this but given that we always pass current_user_ns() we may want to simplify the users of in_user_ns by renaming it current_in_user_ns() and hard codeing current_user_ns(). Eric > Acked-by: Serge Hallyn <serge.hallyn@canonical.com> > Signed-off-by: Seth Forshee <seth.forshee@canonical.com> > --- > include/linux/user_namespace.h | 8 ++++++++ > kernel/user_namespace.c | 14 ++++++++++++++ > security/commoncap.c | 2 ++ > 3 files changed, 24 insertions(+) > > diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h > index 8297e5b341d8..a43faa727124 100644 > --- a/include/linux/user_namespace.h > +++ b/include/linux/user_namespace.h > @@ -72,6 +72,8 @@ 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 in_userns(const struct user_namespace *ns, > + const struct user_namespace *target_ns); > #else > > static inline struct user_namespace *get_user_ns(struct user_namespace *ns) > @@ -100,6 +102,12 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns) > { > return true; > } > + > +static inline bool in_userns(const struct user_namespace *ns, > + const struct user_namespace *target_ns) > +{ > + return true; > +} > #endif > > #endif /* _LINUX_USER_H */ > diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c > index 88fefa68c516..69fbc377357b 100644 > --- a/kernel/user_namespace.c > +++ b/kernel/user_namespace.c > @@ -945,6 +945,20 @@ 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 in_userns(const struct user_namespace *ns, > + const struct user_namespace *target_ns) > +{ > + for (; 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); > diff --git a/security/commoncap.c b/security/commoncap.c > index 1832cf701c3d..400aa224b491 100644 > --- a/security/commoncap.c > +++ b/security/commoncap.c > @@ -450,6 +450,8 @@ 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 (!in_userns(current_user_ns(), 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) { -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Sep 24, 2015 at 04:59:35PM -0500, Eric W. Biederman wrote: > Seth Forshee <seth.forshee@canonical.com> writes: > > > 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, 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. > > No issues with this but given that we always pass current_user_ns() > we may want to simplify the users of in_user_ns by renaming it > current_in_user_ns() and hard codeing current_user_ns(). Sure, if that's what you prefer then I'll change it. Seth -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Seth Forshee <seth.forshee@canonical.com> writes: > On Thu, Sep 24, 2015 at 04:59:35PM -0500, Eric W. Biederman wrote: >> Seth Forshee <seth.forshee@canonical.com> writes: >> >> > 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, 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. >> >> No issues with this but given that we always pass current_user_ns() >> we may want to simplify the users of in_user_ns by renaming it >> current_in_user_ns() and hard codeing current_user_ns(). > > Sure, if that's what you prefer then I'll change it. I took your patch as is. This is a suggestion for a possible incremental improvement. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index 8297e5b341d8..a43faa727124 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -72,6 +72,8 @@ 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 in_userns(const struct user_namespace *ns, + const struct user_namespace *target_ns); #else static inline struct user_namespace *get_user_ns(struct user_namespace *ns) @@ -100,6 +102,12 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns) { return true; } + +static inline bool in_userns(const struct user_namespace *ns, + const struct user_namespace *target_ns) +{ + return true; +} #endif #endif /* _LINUX_USER_H */ diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 88fefa68c516..69fbc377357b 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -945,6 +945,20 @@ 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 in_userns(const struct user_namespace *ns, + const struct user_namespace *target_ns) +{ + for (; 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); diff --git a/security/commoncap.c b/security/commoncap.c index 1832cf701c3d..400aa224b491 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -450,6 +450,8 @@ 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 (!in_userns(current_user_ns(), 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) {