2021-06-09 16:32:45

by Changbin Du

Subject: [PATCH v2] net: do not invoke open_related_ns when NET_NS is disabled

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

The same to tun SIOCGSKNS command.

Signed-off-by: Changbin Du <[email protected]>
Cc: Cong Wang <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: David Laight <[email protected]>
Cc: Christian Brauner <[email protected]>
---
drivers/net/tun.c | 4 ++++
net/socket.c | 4 ++++
2 files changed, 8 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 84f832806313..8ec5977d2f34 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -3003,9 +3003,13 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
} else if (cmd == TUNSETQUEUE) {
return tun_set_queue(file, &ifr);
} else if (cmd == SIOCGSKNS) {
+#ifdef CONFIG_NET_NS
if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
return -EPERM;
return open_related_ns(&net->ns, get_net_ns);
+#else
+ return -EOPNOTSUPP;
+#endif
}

rtnl_lock();
diff --git a/net/socket.c b/net/socket.c
index 27e3e7d53f8e..bc644030d2e8 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);
+#else
+ err = -EOPNOTSUPP;
+#endif
break;
case SIOCGSTAMP_OLD:
case SIOCGSTAMPNS_OLD:
--
2.30.2

2021-06-09 23:13:00

by Jakub Kicinski

Subject: Re: [PATCH v2] net: do not invoke open_related_ns when NET_NS is disabled

On Wed, 9 Jun 2021 23:46:35 +0800 Changbin Du wrote:
> 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
>
> The same to tun SIOCGSKNS command.
>
> Signed-off-by: Changbin Du <[email protected]>
> Cc: Cong Wang <[email protected]>
> Cc: Jakub Kicinski <[email protected]>
> Cc: David Laight <[email protected]>
> Cc: Christian Brauner <[email protected]>
> ---
> drivers/net/tun.c | 4 ++++
> net/socket.c | 4 ++++
> 2 files changed, 8 insertions(+)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 84f832806313..8ec5977d2f34 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -3003,9 +3003,13 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
> } else if (cmd == TUNSETQUEUE) {
> return tun_set_queue(file, &ifr);
> } else if (cmd == SIOCGSKNS) {
> +#ifdef CONFIG_NET_NS
> if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> return -EPERM;
> return open_related_ns(&net->ns, get_net_ns);
> +#else
> + return -EOPNOTSUPP;
> +#endif

... and why are you not adding that check to get_net_ns like
I suggested twice and even shared a diff?