[PATCH] net: always initialize sysctl ownership

[PATCH] net: always initialize sysctl ownership

[Thomas Weißschuh]

The sysctl core does not initialize these fields when the set_ownership
callback is present.
So always do it in the callback.

Fixes: e79c6a4fc923 ("net: make net namespace sysctls belong to container's owner")
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 net/sysctl_net.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/sysctl_net.c b/net/sysctl_net.c
index 051ed5f6fc93..03e320ddacc9 100644
--- a/net/sysctl_net.c
+++ b/net/sysctl_net.c
@@ -62,12 +62,10 @@ static void net_ctl_set_ownership(struct ctl_table_header *head,
 	kgid_t ns_root_gid;
 
 	ns_root_uid = make_kuid(net->user_ns, 0);
-	if (uid_valid(ns_root_uid))
-		*uid = ns_root_uid;
+	*uid = uid_valid(ns_root_uid) ? ns_root_uid : GLOBAL_ROOT_UID;
 
 	ns_root_gid = make_kgid(net->user_ns, 0);
-	if (gid_valid(ns_root_gid))
-		*gid = ns_root_gid;
+	*gid = gid_valid(ns_root_gid) ? ns_root_gid : GLOBAL_ROOT_GID;
 }
 
 static struct ctl_table_root net_sysctl_root = {

---
base-commit: e5eb28f6d1afebed4bb7d740a797d0390bd3a357
change-id: 20240315-sysctl-net-ownership-bc4e17eaeea6

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>

Re: [PATCH] net: always initialize sysctl ownership

[Kuniyuki Iwashima]

From: Thomas Weißschuh <linux@weissschuh.net>
Date: Fri, 15 Mar 2024 17:20:31 +0100
> The sysctl core does not initialize these fields when the set_ownership
> callback is present.
> So always do it in the callback.

Could you add few more words here to explain what the problem is
like commit 5ec27ec735ba ("fs/proc/proc_sysctl.c: fix the default
values of i_uid/i_gid on /proc/sys inodes.").

BTW, it seems that we can change the value even if the uid/gid is
invalid unlike the issue mentioned in 5ec27ec735ba.

So, the problem is just the invalid uid/gid exposed to userspace
or am I missing something ?

---8<---
[root@localhost ~]# unshare --user --keep-caps
[nobody@localhost ~]$ id
uid=65534(nobody) gid=65534(nobody) groups=65534(nobody)
[nobody@localhost ~]$ unshare --net --keep-caps
[nobody@localhost ~]$ stat /proc/sys/net/core/somaxconn
  File: /proc/sys/net/core/somaxconn
  Size: 0         	Blocks: 0          IO Block: 1024   regular empty file
Device: 13h/19d	Inode: 3726        Links: 1
Access: (0644/-rw-r--r--)  Uid: (65534/  nobody)   Gid: (65534/  nobody)
Access: 2024-03-16 00:28:51.937789000 +0000
Modify: 2024-03-16 00:28:51.937789000 +0000
Change: 2024-03-16 00:28:51.937789000 +0000
 Birth: -
[nobody@localhost ~]$ cat /proc/sys/net/core/somaxconn
4096
[nobody@localhost ~]$ echo 2048 > /proc/sys/net/core/somaxconn
[nobody@localhost ~]$ cat /proc/sys/net/core/somaxconn
2048
---8<---


> 
> Fixes: e79c6a4fc923 ("net: make net namespace sysctls belong to container's owner")
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
>  net/sysctl_net.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sysctl_net.c b/net/sysctl_net.c
> index 051ed5f6fc93..03e320ddacc9 100644
> --- a/net/sysctl_net.c
> +++ b/net/sysctl_net.c
> @@ -62,12 +62,10 @@ static void net_ctl_set_ownership(struct ctl_table_header *head,
>  	kgid_t ns_root_gid;
>  
>  	ns_root_uid = make_kuid(net->user_ns, 0);
> -	if (uid_valid(ns_root_uid))
> -		*uid = ns_root_uid;
> +	*uid = uid_valid(ns_root_uid) ? ns_root_uid : GLOBAL_ROOT_UID;
>  
>  	ns_root_gid = make_kgid(net->user_ns, 0);
> -	if (gid_valid(ns_root_gid))
> -		*gid = ns_root_gid;
> +	*gid = gid_valid(ns_root_gid) ? ns_root_gid : GLOBAL_ROOT_GID;
>  }

How about setting the default in proc_sys_make_inode() instead ?
because the default value configured by new_inode() is not
appropriate for procfs, IIUC.

Thanks!

>  
>  static struct ctl_table_root net_sysctl_root = {
> 
> ---
> base-commit: e5eb28f6d1afebed4bb7d740a797d0390bd3a357
> change-id: 20240315-sysctl-net-ownership-bc4e17eaeea6
> 
> Best regards,
> -- 
> Thomas Weißschuh <linux@weissschuh.net>

Re: [PATCH] net: always initialize sysctl ownership

[Joel Granados]

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On Fri, Mar 15, 2024 at 05:39:58PM -0700, Kuniyuki Iwashima wrote:
> From: Thomas Weißschuh <linux@weissschuh.net>
> Date: Fri, 15 Mar 2024 17:20:31 +0100
> > The sysctl core does not initialize these fields when the set_ownership
> > callback is present.
> > So always do it in the callback.
> 
> Could you add few more words here to explain what the problem is
> like commit 5ec27ec735ba ("fs/proc/proc_sysctl.c: fix the default
> values of i_uid/i_gid on /proc/sys inodes.").
I second this proposal. There is more to the story than a simple setting
of default values. IMO, you should mention how the missbehavior was
introduced in 5ec27ec735ba0 (fs/proc/proc_sysctl.c: fix the default
values of i_uid/i_gid on /proc/sys inodes.)

> 
> BTW, it seems that we can change the value even if the uid/gid is
> invalid unlike the issue mentioned in 5ec27ec735ba.
Indeed and I think it is because net_ctl_permissions set the mode in the
same way as test_perm does. Therefore regardless of the tests against
GLOBAL_ROOT_[U|G]ID being true or false mode gets right shifted by 6 and
3.

> 
> So, the problem is just the invalid uid/gid exposed to userspace
> or am I missing something ?
That seems to be the case. I think that should just be
GLOBAL_ROOT_[G|U]ID. Please correct me if I'm wrong.

> 
> ---8<---
> [root@localhost ~]# unshare --user --keep-caps
> [nobody@localhost ~]$ id
> uid=65534(nobody) gid=65534(nobody) groups=65534(nobody)
> [nobody@localhost ~]$ unshare --net --keep-caps
> [nobody@localhost ~]$ stat /proc/sys/net/core/somaxconn
>   File: /proc/sys/net/core/somaxconn
>   Size: 0         	Blocks: 0          IO Block: 1024   regular empty file
> Device: 13h/19d	Inode: 3726        Links: 1
> Access: (0644/-rw-r--r--)  Uid: (65534/  nobody)   Gid: (65534/  nobody)
> Access: 2024-03-16 00:28:51.937789000 +0000
> Modify: 2024-03-16 00:28:51.937789000 +0000
> Change: 2024-03-16 00:28:51.937789000 +0000
>  Birth: -
> [nobody@localhost ~]$ cat /proc/sys/net/core/somaxconn
> 4096
> [nobody@localhost ~]$ echo 2048 > /proc/sys/net/core/somaxconn
> [nobody@localhost ~]$ cat /proc/sys/net/core/somaxconn
> 2048
> ---8<---
> 
> 
> > 
> > Fixes: e79c6a4fc923 ("net: make net namespace sysctls belong to container's owner")
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> > ---
> >  net/sysctl_net.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff --git a/net/sysctl_net.c b/net/sysctl_net.c
> > index 051ed5f6fc93..03e320ddacc9 100644
> > --- a/net/sysctl_net.c
> > +++ b/net/sysctl_net.c
> > @@ -62,12 +62,10 @@ static void net_ctl_set_ownership(struct ctl_table_header *head,
> >  	kgid_t ns_root_gid;
> >  
> >  	ns_root_uid = make_kuid(net->user_ns, 0);
> > -	if (uid_valid(ns_root_uid))
> > -		*uid = ns_root_uid;
> > +	*uid = uid_valid(ns_root_uid) ? ns_root_uid : GLOBAL_ROOT_UID;
> >  
> >  	ns_root_gid = make_kgid(net->user_ns, 0);
> > -	if (gid_valid(ns_root_gid))
> > -		*gid = ns_root_gid;
> > +	*gid = gid_valid(ns_root_gid) ? ns_root_gid : GLOBAL_ROOT_GID;
> >  }
> 
> How about setting the default in proc_sys_make_inode() instead ?
> because the default value configured by new_inode() is not
> appropriate for procfs, IIUC.
Are you proposing something like this in proc_sys_make_inode/

inode->i_uid = GLOBAL_ROOT_UID;
inode->i_gid = GLOBAL_ROOT_GID;
if (root->set_ownership)
    root->set_ownership(head, table, &indoe->i_uid, &inode->i_gid)

?

> 
> Thanks!
> 
> >  
> >  static struct ctl_table_root net_sysctl_root = {
> > 
> > ---
> > base-commit: e5eb28f6d1afebed4bb7d740a797d0390bd3a357
> > change-id: 20240315-sysctl-net-ownership-bc4e17eaeea6
> > 
> > Best regards,
> > -- 
> > Thomas Weißschuh <linux@weissschuh.net>

-- 

Joel Granados

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Re: [PATCH] net: always initialize sysctl ownership

[Paolo Abeni]

On Fri, 2024-03-15 at 17:39 -0700, Kuniyuki Iwashima wrote:
> on Fri, 15 Mar 2024 17:20:31 +0100 Thomas Weißschuh <linux@weissschuh.net wrote:
> 
> > diff --git a/net/sysctl_net.c b/net/sysctl_net.c
> > index 051ed5f6fc93..03e320ddacc9 100644
> > --- a/net/sysctl_net.c
> > +++ b/net/sysctl_net.c
> > @@ -62,12 +62,10 @@ static void net_ctl_set_ownership(struct ctl_table_header *head,
> >  	kgid_t ns_root_gid;
> >  
> >  	ns_root_uid = make_kuid(net->user_ns, 0);
> > -	if (uid_valid(ns_root_uid))
> > -		*uid = ns_root_uid;
> > +	*uid = uid_valid(ns_root_uid) ? ns_root_uid : GLOBAL_ROOT_UID;
> >  
> >  	ns_root_gid = make_kgid(net->user_ns, 0);
> > -	if (gid_valid(ns_root_gid))
> > -		*gid = ns_root_gid;
> > +	*gid = gid_valid(ns_root_gid) ? ns_root_gid : GLOBAL_ROOT_GID;
> >  }
> 
> How about setting the default in proc_sys_make_inode() instead ?
> because the default value configured by new_inode() is not

I also think that could be a better option, as the caller is already
providing default values in some cases.

Cheers,

Paolo

Re: [PATCH] net: always initialize sysctl ownership

[Joel Granados]

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On Fri, Mar 15, 2024 at 05:20:31PM +0100, Thomas Weißschuh wrote:
> The sysctl core does not initialize these fields when the set_ownership
> callback is present.
This is a bit ambiguous as these values get set in the new_inode(sb)
call. What is really happening is that the GLOBAL_ROOT_[U|G]ID is not
getting the correct default.

> So always do it in the callback.
> 
> Fixes: e79c6a4fc923 ("net: make net namespace sysctls belong to container's owner")
I think this is incorrect and here is why:
1. At the point of committing this code, the default behavior was
   dictated by the new_inode call. Which calculated the value from
   super_block *sb. This was Aug 10 2016 (approx).
2. The issue comes when a new default behavior is added by setting
   GLOBAL_ROOT_[U|G]ID in 5ec27ec735ba0 ("fs/proc/proc_sysctl.c: fix the
   default values of i_uid/i_gid on /proc/sys inodes"). This commit was
   in 2019 and missed adjusting net_ctl_set_ownership.

> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
>  net/sysctl_net.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sysctl_net.c b/net/sysctl_net.c
> index 051ed5f6fc93..03e320ddacc9 100644
> --- a/net/sysctl_net.c
> +++ b/net/sysctl_net.c
> @@ -62,12 +62,10 @@ static void net_ctl_set_ownership(struct ctl_table_header *head,
>  	kgid_t ns_root_gid;
>  
>  	ns_root_uid = make_kuid(net->user_ns, 0);
> -	if (uid_valid(ns_root_uid))
> -		*uid = ns_root_uid;
> +	*uid = uid_valid(ns_root_uid) ? ns_root_uid : GLOBAL_ROOT_UID;
>  
>  	ns_root_gid = make_kgid(net->user_ns, 0);
> -	if (gid_valid(ns_root_gid))
> -		*gid = ns_root_gid;
> +	*gid = gid_valid(ns_root_gid) ? ns_root_gid : GLOBAL_ROOT_GID;
>  }
>  
>  static struct ctl_table_root net_sysctl_root = {
> 
> ---
> base-commit: e5eb28f6d1afebed4bb7d740a797d0390bd3a357
> change-id: 20240315-sysctl-net-ownership-bc4e17eaeea6
> 
> Best regards,
> -- 
> Thomas Weißschuh <linux@weissschuh.net>
> 

-- 

Joel Granados

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