This is a note to let you know that I've just added the patch titled userns: Don't allow setgroups until a gid mapping has been setablished to the 3.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: userns-don-t-allow-setgroups-until-a-gid-mapping-has-been-setablished.patch and it can be found in the queue-3.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 273d2c67c3e179adb1e74f403d1e9a06e3f841b5 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Date: Fri, 5 Dec 2014 18:01:11 -0600 Subject: userns: Don't allow setgroups until a gid mapping has been setablished From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> commit 273d2c67c3e179adb1e74f403d1e9a06e3f841b5 upstream. setgroups is unique in not needing a valid mapping before it can be called, in the case of setgroups(0, NULL) which drops all supplemental groups. The design of the user namespace assumes that CAP_SETGID can not actually be used until a gid mapping is established. Therefore add a helper function to see if the user namespace gid mapping has been established and call that function in the setgroups permission check. This is part of the fix for CVE-2014-8989, being able to drop groups without privilege using user namespaces. Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/linux/user_namespace.h | 5 +++++ kernel/groups.c | 4 +++- kernel/user_namespace.c | 14 ++++++++++++++ 3 files changed, 22 insertions(+), 1 deletion(-) --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -63,6 +63,7 @@ extern struct seq_operations proc_projid extern ssize_t proc_uid_map_write(struct file *, const char __user *, size_t, loff_t *); extern ssize_t proc_gid_map_write(struct file *, const char __user *, size_t, loff_t *); extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, loff_t *); +extern bool userns_may_setgroups(const struct user_namespace *ns); #else static inline struct user_namespace *get_user_ns(struct user_namespace *ns) @@ -87,6 +88,10 @@ static inline void put_user_ns(struct us { } +static inline bool userns_may_setgroups(const struct user_namespace *ns) +{ + return true; +} #endif #endif /* _LINUX_USER_H */ --- a/kernel/groups.c +++ b/kernel/groups.c @@ -6,6 +6,7 @@ #include <linux/slab.h> #include <linux/security.h> #include <linux/syscalls.h> +#include <linux/user_namespace.h> #include <asm/uaccess.h> /* init to 2 - one for init_task, one to ensure it is never freed */ @@ -227,7 +228,8 @@ bool may_setgroups(void) { struct user_namespace *user_ns = current_user_ns(); - return ns_capable(user_ns, CAP_SETGID); + return ns_capable(user_ns, CAP_SETGID) && + userns_may_setgroups(user_ns); } /* --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -836,6 +836,20 @@ static bool new_idmap_permitted(const st return false; } +bool userns_may_setgroups(const struct user_namespace *ns) +{ + bool allowed; + + mutex_lock(&id_map_mutex); + /* It is not safe to use setgroups until a gid mapping in + * the user namespace has been established. + */ + allowed = ns->gid_map.nr_extents != 0; + mutex_unlock(&id_map_mutex); + + return allowed; +} + static void *userns_get(struct task_struct *task) { struct user_namespace *user_ns; Patches currently in stable-queue which might be from ebiederm@xxxxxxxxxxxx are queue-3.14/mnt-update-unprivileged-remount-test.patch queue-3.14/mnt-fix-a-memory-stomp-in-umount.patch queue-3.14/userns-check-euid-no-fsuid-when-establishing-an-unprivileged-uid-mapping.patch queue-3.14/mnt-implicitly-add-mnt_nodev-on-remount-when-it-was-implicitly-added-by-mount.patch queue-3.14/userns-don-t-allow-unprivileged-creation-of-gid-mappings.patch queue-3.14/userns-rename-id_map_mutex-to-userns_state_mutex.patch queue-3.14/userns-add-a-knob-to-disable-setgroups-on-a-per-user-namespace-basis.patch queue-3.14/userns-allow-setting-gid_maps-without-privilege-when-setgroups-is-disabled.patch queue-3.14/userns-don-t-allow-setgroups-until-a-gid-mapping-has-been-setablished.patch queue-3.14/groups-consolidate-the-setgroups-permission-checks.patch queue-3.14/userns-only-allow-the-creator-of-the-userns-unprivileged-mappings.patch queue-3.14/userns-document-what-the-invariant-required-for-safe-unprivileged-mappings.patch queue-3.14/umount-disallow-unprivileged-mount-force.patch queue-3.14/userns-unbreak-the-unprivileged-remount-tests.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html