On Mon, May 31, 2021 at 10:01 PM Jakub Kicinski kuba@kernel.org wrote:
On Mon, 31 May 2021 23:34:10 +0800 Changbin Du wrote:
We should not create inode for disabled namespace. A disabled namespace sets its ns->ops to NULL. Kernel could panic if we try to create a inode for such namespace.
Here is an example oops in socket ioctl cmd SIOCGSKNS when NET_NS is disabled. Kernel panicked wherever nsfs trys to access ns->ops since the proc_ns_operations is not implemented in this case.
[7.670023] Unable to handle kernel NULL pointer dereference at virtual address 00000010 [7.670268] pgd = 32b54000 [7.670544] [00000010] *pgd=00000000 [7.671861] Internal error: Oops: 5 [#1] SMP ARM [7.672315] Modules linked in: [7.672918] CPU: 0 PID: 1 Comm: systemd Not tainted 5.13.0-rc3-00375-g6799d4f2da49 #16 [7.673309] Hardware name: Generic DT based system [7.673642] PC is at nsfs_evict+0x24/0x30 [7.674486] LR is at clear_inode+0x20/0x9c
So let's reject such request for disabled namespace.
Signed-off-by: Changbin Du changbin.du@gmail.com Cc: stable@vger.kernel.org Cc: Cong Wang xiyou.wangcong@gmail.com Cc: Jakub Kicinski kuba@kernel.org Cc: David Laight David.Laight@ACULAB.COM
fs/nsfs.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/fs/nsfs.c b/fs/nsfs.c index 800c1d0eb0d0..6c055eb7757b 100644 --- a/fs/nsfs.c +++ b/fs/nsfs.c @@ -62,6 +62,10 @@ static int __ns_get_path(struct path *path, struct ns_common *ns) struct inode *inode; unsigned long d;
/* In case the namespace is not actually enabled. */
if (!ns->ops)
return -EOPNOTSUPP;
rcu_read_lock(); d = atomic_long_read(&ns->stashed); if (!d)
I'm not sure why we'd pick runtime checks for something that can be perfectly easily solved at compilation time. Networking should not be asking for FDs for objects which don't exist.
Four reasons:
1) ioctl() is not a hot path, so performance is not a problem here.
2) There are 3 different places (tun has two more) that need the same fix.
3) init_net always exits, except it does not have an ops when CONFIG_NET_NS is disabled:
static __net_init int net_ns_net_init(struct net *net) { #ifdef CONFIG_NET_NS net->ns.ops = &netns_operations; #endif return ns_alloc_inum(&net->ns); }
4) *I think* other namespaces need this fix too, for instance init_ipc_ns:
struct ipc_namespace init_ipc_ns = { .ns.count = REFCOUNT_INIT(1), .user_ns = &init_user_ns, .ns.inum = PROC_IPC_INIT_INO, #ifdef CONFIG_IPC_NS .ns.ops = &ipcns_operations, #endif };
whose ns->ops is NULL too if disabled.
Thanks.