Re: [PATCH] net: fix oops in socket ioctl cmd SIOCGSKNS when NET_NS is disabled

On Sat, May 29, 2021 at 11:27:35AM -0700, Jakub Kicinski wrote:

On Sat, 29 May 2021 14:05:26 +0800 Changbin Du wrote:

quoted

When NET_NS is not enabled, socket ioctl cmd SIOCGSKNS should do nothing
but acknowledge userspace it is not supported. Otherwise, kernel would
panic 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

Signed-off-by: Changbin Du <redacted>
Cc: <redacted> # v4.9

Please provide a Fixes tag.

Now it will be fixed by nsfs side. And the code has been changed to many times..

quoted

diff --git a/net/socket.c b/net/socket.c
index 27e3e7d53f8e..644b46112d35 100644
--- a/net/socket.c
+++ b/net/socket.c

@@ -1149,11 +1149,15 @@ static long sock_ioctl(struct file *file, unsigned cmd, unsigned long arg)
 			mutex_unlock(&vlan_ioctl_mutex);
 			break;
 		case SIOCGSKNS:
+#ifdef CONFIG_NET_NS
 			err = -EPERM;
 			if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
 				break;
 
 			err = open_related_ns(&net->ns, get_net_ns);

There's a few more places with this exact code. Can we please add the
check in get_net_ns? That should fix all callers.

quoted

+#else
+			err = -ENOTSUPP;

EOPNOTSUPP, you shouldn't return ENOTSUPP to user space.

Thanks for pointing out. Will change it.

quoted

+#endif
 			break;
 		case SIOCGSTAMP_OLD:
 		case SIOCGSTAMPNS_OLD:

-- 
Cheers,
Changbin Du