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Date: Thu, 21 Oct 2021 11:20:44 +0200 From: Christian Brauner <christian.brauner@...ntu.com> To: Sargun Dhillon <sargun@...gun.me> Cc: Sergey Ryazanov <ryazanov.s.a@...il.com>, LKML <linux-kernel@...r.kernel.org>, netdev <netdev@...r.kernel.org> Subject: Re: Retrieving the network namespace of a socket On Wed, Oct 20, 2021 at 07:24:57PM +0000, Sargun Dhillon wrote: > On Wed, Oct 20, 2021 at 04:34:18PM +0000, Sargun Dhillon wrote: > > On Wed, Oct 20, 2021 at 05:03:56PM +0300, Sergey Ryazanov wrote: > > > Hello Sargun, > > > > > > On Wed, Oct 20, 2021 at 12:57 PM Sargun Dhillon <sargun@...gun.me> wrote: > > > > I'm working on a problem where I need to determine which network namespace a > > > > given socket is in. I can currently bruteforce this by using INET_DIAG, and > > > > enumerating namespaces and working backwards. > > > > > > Namespace is not a per-socket, but a per-process attribute. So each > > > socket of a process belongs to the same namespace. > > > > > > Could you elaborate what kind of problem you are trying to solve? > > > Maybe there is a more simple solution. for it. > > > > > > -- > > > Sergey > > > > That's not entirely true. See the folowing code: > > > > int main() { > > int fd1, fd2; > > fd1 = socket(AF_INET, SOCK_STREAM, 0); > > assert(fd1 >= 0); > > assert(unshare(CLONE_NEWNET) == 0); > > fd2 = socket(AF_INET, SOCK_STREAM, 0); > > assert(fd2 >= 0); > > } > > > > fd1 and fd2 have different sock_net. > > > > The context for this is: > > https://linuxplumbersconf.org/event/11/contributions/932/ > > > > We need to figure out, for a given socket, if it has reachability to a given IP. > > So, I was lazy / misread documentation. It turns out SIOCGSKNS does exactly > what I need. I was about to reply with this. :) It's heavily used in CRIU and we use it in LXC/LXD as well. > > Nonetheless, it's a little weird and awkward that it is exists. I was wondering > if this functionality made sense as part of kcmp. I wrote up a quick patch > to see if anyone was interested: Per se I don't see a reason why this shouldn't exist as an extension to kcmp(). It seems useful. > > diff --git a/include/uapi/linux/kcmp.h b/include/uapi/linux/kcmp.h > index ef1305010925..d6b9c3923d20 100644 > --- a/include/uapi/linux/kcmp.h > +++ b/include/uapi/linux/kcmp.h > @@ -14,6 +14,7 @@ enum kcmp_type { > KCMP_IO, > KCMP_SYSVSEM, > KCMP_EPOLL_TFD, > + KCMP_NETNS, > > KCMP_TYPES, > }; > diff --git a/kernel/kcmp.c b/kernel/kcmp.c > index 5353edfad8e1..8fadae4b588f 100644 > --- a/kernel/kcmp.c > +++ b/kernel/kcmp.c > @@ -18,6 +18,8 @@ > #include <linux/file.h> > > #include <asm/unistd.h> > +#include <net/net_namespace.h> > +#include <net/sock.h> > > /* > * We don't expose the real in-memory order of objects for security reasons. > @@ -132,6 +134,58 @@ static int kcmp_epoll_target(struct task_struct *task1, > } > #endif > > +#ifdef CONFIG_NET > +static int __kcmp_netns_target(struct task_struct *task1, > + struct task_struct *task2, > + struct file *filp1, > + struct file *filp2) > +{ > + struct socket *sock1, *sock2; > + struct net *net1, *net2; > + > + sock1 = sock_from_file(filp1); > + sock2 = sock_from_file(filp1); > + if (!sock1 || !sock2) > + return -ENOTSOCK; > + > + net1 = sock_net(sock1->sk); > + net2 = sock_net(sock2->sk); > + > + return kcmp_ptr(net1, net2, KCMP_NETNS); > +} > + > +static int kcmp_netns_target(struct task_struct *task1, > + struct task_struct *task2, > + unsigned long idx1, > + unsigned long idx2) > +{ > + struct file *filp1, *filp2; > + > + int ret = -EBADF; > + > + filp1 = fget_task(task1, idx1); > + if (filp1) { > + filp2 = fget_task(task2, idx2); > + if (filp2) { > + ret = __kcmp_netns_target(task1, task2, filp1, filp2); > + fput(filp2); > + } > + > + fput(filp1); > + } > + > + return ret; > +} > +#else > +static int kcmp_netns_target(struct task_struct *task1, > + struct task_struct *task2, > + unsigned long idx1, > + unsigned long idx2) > +{ > + return -EOPNOTSUPP; > +} > +#endif > + > SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type, > unsigned long, idx1, unsigned long, idx2) > { > @@ -206,6 +260,9 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type, > case KCMP_EPOLL_TFD: > ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2); > break; > + case KCMP_NETNS: > + ret = kcmp_netns_target(task1, task2, idx1, idx2); > + break; > default: > ret = -EINVAL; > break; >
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