99 lines
3.2 KiB
Diff
99 lines
3.2 KiB
Diff
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From: "Eric W. Biederman" <ebiederm@xmission.com>
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Date: Fri, 5 Dec 2014 18:01:11 -0600
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Subject: [PATCH] userns: Don't allow setgroups until a gid mapping has been
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setablished
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setgroups is unique in not needing a valid mapping before it can be called,
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in the case of setgroups(0, NULL) which drops all supplemental groups.
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The design of the user namespace assumes that CAP_SETGID can not actually
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be used until a gid mapping is established. Therefore add a helper function
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to see if the user namespace gid mapping has been established and call
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that function in the setgroups permission check.
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This is part of the fix for CVE-2014-8989, being able to drop groups
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without privilege using user namespaces.
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Cc: stable@vger.kernel.org
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Reviewed-by: Andy Lutomirski <luto@amacapital.net>
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Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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---
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include/linux/user_namespace.h | 5 +++++
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kernel/groups.c | 4 +++-
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kernel/user_namespace.c | 14 ++++++++++++++
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3 files changed, 22 insertions(+), 1 deletion(-)
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diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
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index e95372654f09..8d493083486a 100644
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--- a/include/linux/user_namespace.h
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+++ b/include/linux/user_namespace.h
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@@ -63,6 +63,7 @@ extern const struct seq_operations proc_projid_seq_operations;
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extern ssize_t proc_uid_map_write(struct file *, const char __user *, size_t, loff_t *);
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extern ssize_t proc_gid_map_write(struct file *, const char __user *, size_t, loff_t *);
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extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, loff_t *);
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+extern bool userns_may_setgroups(const struct user_namespace *ns);
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#else
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static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
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@@ -87,6 +88,10 @@ static inline void put_user_ns(struct user_namespace *ns)
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{
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}
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+static inline bool userns_may_setgroups(const struct user_namespace *ns)
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+{
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+ return true;
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+}
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#endif
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#endif /* _LINUX_USER_H */
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diff --git a/kernel/groups.c b/kernel/groups.c
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index 02d8a251c476..664411f171b5 100644
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--- a/kernel/groups.c
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+++ b/kernel/groups.c
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@@ -6,6 +6,7 @@
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#include <linux/slab.h>
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#include <linux/security.h>
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#include <linux/syscalls.h>
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+#include <linux/user_namespace.h>
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#include <asm/uaccess.h>
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/* init to 2 - one for init_task, one to ensure it is never freed */
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@@ -217,7 +218,8 @@ bool may_setgroups(void)
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{
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struct user_namespace *user_ns = current_user_ns();
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- return ns_capable(user_ns, CAP_SETGID);
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+ return ns_capable(user_ns, CAP_SETGID) &&
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+ userns_may_setgroups(user_ns);
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}
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/*
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diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
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index b99c862a2e3f..27c8dab48c07 100644
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--- a/kernel/user_namespace.c
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+++ b/kernel/user_namespace.c
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@@ -843,6 +843,20 @@ static bool new_idmap_permitted(const struct file *file,
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return false;
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}
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+bool userns_may_setgroups(const struct user_namespace *ns)
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+{
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+ bool allowed;
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+
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+ mutex_lock(&id_map_mutex);
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+ /* It is not safe to use setgroups until a gid mapping in
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+ * the user namespace has been established.
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+ */
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+ allowed = ns->gid_map.nr_extents != 0;
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+ mutex_unlock(&id_map_mutex);
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+
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+ return allowed;
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+}
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+
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static void *userns_get(struct task_struct *task)
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{
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struct user_namespace *user_ns;
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--
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2.1.0
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