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| author | Eric W. Biederman <ebiederm@xmission.com> | 2013-03-13 11:51:49 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-03-13 15:00:20 -0700 |
| commit | e66eded8309ebf679d3d3c1f5820d1f2ca332c71 (patch) | |
| tree | 768e1d799f6d6a4a7f85f48d9e9fc431dc8d017c /kernel | |
| parent | 6c23cbbd5056b155401b0a2b5567d530e6c750c4 (diff) | |
| download | lwn-e66eded8309ebf679d3d3c1f5820d1f2ca332c71.tar.gz lwn-e66eded8309ebf679d3d3c1f5820d1f2ca332c71.zip | |
userns: Don't allow CLONE_NEWUSER | CLONE_FS
Don't allowing sharing the root directory with processes in a
different user namespace. There doesn't seem to be any point, and to
allow it would require the overhead of putting a user namespace
reference in fs_struct (for permission checks) and incrementing that
reference count on practically every call to fork.
So just perform the inexpensive test of forbidding sharing fs_struct
acrosss processes in different user namespaces. We already disallow
other forms of threading when unsharing a user namespace so this
should be no real burden in practice.
This updates setns, clone, and unshare to disallow multiple user
namespaces sharing an fs_struct.
Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/fork.c | 5 | ||||
| -rw-r--r-- | kernel/user_namespace.c | 4 |
2 files changed, 8 insertions, 1 deletions
diff --git a/kernel/fork.c b/kernel/fork.c index 8d932b1c9056..1766d324d5e3 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1141,6 +1141,9 @@ static struct task_struct *copy_process(unsigned long clone_flags, if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS)) return ERR_PTR(-EINVAL); + if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS)) + return ERR_PTR(-EINVAL); + /* * Thread groups must share signals as well, and detached threads * can only be started up within the thread group. @@ -1807,7 +1810,7 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) * If unsharing a user namespace must also unshare the thread. */ if (unshare_flags & CLONE_NEWUSER) - unshare_flags |= CLONE_THREAD; + unshare_flags |= CLONE_THREAD | CLONE_FS; /* * If unsharing a pid namespace must also unshare the thread. */ diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 8b650837083e..b14f4d342043 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -21,6 +21,7 @@ #include <linux/uaccess.h> #include <linux/ctype.h> #include <linux/projid.h> +#include <linux/fs_struct.h> static struct kmem_cache *user_ns_cachep __read_mostly; @@ -837,6 +838,9 @@ static int userns_install(struct nsproxy *nsproxy, void *ns) if (atomic_read(¤t->mm->mm_users) > 1) return -EINVAL; + if (current->fs->users != 1) + return -EINVAL; + if (!ns_capable(user_ns, CAP_SYS_ADMIN)) return -EPERM; |