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| author | Eric W. Biederman <ebiederm@xmission.com> | 2014-12-06 01:01:11 +0100 |
|---|---|---|
| committer | Eric W. Biederman <ebiederm@xmission.com> | 2014-12-09 23:58:40 +0100 |
| commit | 273d2c67c3e179adb1e74f403d1e9a06e3f841b5 (patch) | |
| tree | 500bf14c930ea5c1db4c40dec54d95a00085552c /kernel | |
| parent | userns: Document what the invariant required for safe unprivileged mappings. (diff) | |
| download | linux-273d2c67c3e179adb1e74f403d1e9a06e3f841b5.tar.xz linux-273d2c67c3e179adb1e74f403d1e9a06e3f841b5.zip | |
userns: Don't allow setgroups until a gid mapping has been setablished
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.
Cc: stable@vger.kernel.org
Reviewed-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/groups.c | 4 | ||||
| -rw-r--r-- | kernel/user_namespace.c | 14 |
2 files changed, 17 insertions, 1 deletions
diff --git a/kernel/groups.c b/kernel/groups.c index 02d8a251c476..664411f171b5 100644 --- 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 */ @@ -217,7 +218,8 @@ 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); } /* diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index b99c862a2e3f..27c8dab48c07 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -843,6 +843,20 @@ static bool new_idmap_permitted(const struct file *file, 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; |