From: Matteo Croce <teknoraver@meta.com>

The following sysctl are global and can't be read from a netns:

net.core.rmem_default
net.core.rmem_max
net.core.wmem_default
net.core.wmem_max

Make the following sysctl parameters available readonly from within a
network namespace, allowing a container to read them.

Signed-off-by: Matteo Croce <teknoraver@meta.com>
---
 net/core/sysctl_net_core.c | 75 +++++++++++++++++++++-----------------
 1 file changed, 42 insertions(+), 33 deletions(-)

diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index c9fb9ad87485..2079000691e2 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -382,38 +382,6 @@ proc_dolongvec_minmax_bpf_restricted(struct ctl_table *table, int write,
 #endif
 
 static struct ctl_table net_core_table[] = {
-	{
-		.procname	= "wmem_max",
-		.data		= &sysctl_wmem_max,
-		.maxlen		= sizeof(int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &min_sndbuf,
-	},
-	{
-		.procname	= "rmem_max",
-		.data		= &sysctl_rmem_max,
-		.maxlen		= sizeof(int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &min_rcvbuf,
-	},
-	{
-		.procname	= "wmem_default",
-		.data		= &sysctl_wmem_default,
-		.maxlen		= sizeof(int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &min_sndbuf,
-	},
-	{
-		.procname	= "rmem_default",
-		.data		= &sysctl_rmem_default,
-		.maxlen		= sizeof(int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &min_rcvbuf,
-	},
 	{
 		.procname	= "mem_pcpu_rsv",
 		.data		= &net_hotdata.sysctl_mem_pcpu_rsv,
@@ -697,6 +665,41 @@ static struct ctl_table netns_core_table[] = {
 		.extra2		= SYSCTL_ONE,
 		.proc_handler	= proc_dou8vec_minmax,
 	},
+	/* sysctl_core_net_init() will set the values after this
+	 * to readonly in network namespaces
+	 */
+	{
+		.procname	= "wmem_max",
+		.data		= &sysctl_wmem_max,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &min_sndbuf,
+	},
+	{
+		.procname	= "rmem_max",
+		.data		= &sysctl_rmem_max,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &min_rcvbuf,
+	},
+	{
+		.procname	= "wmem_default",
+		.data		= &sysctl_wmem_default,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &min_sndbuf,
+	},
+	{
+		.procname	= "rmem_default",
+		.data		= &sysctl_rmem_default,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &min_rcvbuf,
+	},
 };
 
 static int __init fb_tunnels_only_for_init_net_sysctl_setup(char *str)
@@ -724,8 +727,14 @@ static __net_init int sysctl_core_net_init(struct net *net)
 		if (tbl == NULL)
 			goto err_dup;
 
-		for (i = 0; i < table_size; ++i)
+		for (i = 0; i < table_size; ++i) {
+			if (tbl[i].data == &sysctl_wmem_max)
+				break;
+
 			tbl[i].data += (char *)net - (char *)&init_net;
+		}
+		for (; i < table_size; ++i)
+			tbl[i].mode &= ~0222;
 	}
 
 	net->core.sysctl_hdr = register_net_sysctl_sz(net, "net/core", tbl, table_size);
-- 
2.45.1

On Fri, May 31, 2024 at 01:27:21AM GMT, technoboy85@gmail.com wrote:
> From: Matteo Croce <teknoraver@meta.com>
> 
> The following sysctl are global and can't be read from a netns:
> 
> net.core.rmem_default
> net.core.rmem_max
> net.core.wmem_default
> net.core.wmem_max
> 
> Make the following sysctl parameters available readonly from within a
> network namespace, allowing a container to read them.
> 
> Signed-off-by: Matteo Croce <teknoraver@meta.com>

Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>

On Fri, May 31, 2024 at 1:27 AM <technoboy85@gmail.com> wrote:
>
> From: Matteo Croce <teknoraver@meta.com>
>
> The following sysctl are global and can't be read from a netns:
>
> net.core.rmem_default
> net.core.rmem_max
> net.core.wmem_default
> net.core.wmem_max
>
> Make the following sysctl parameters available readonly from within a
> network namespace, allowing a container to read them.
>
> Signed-off-by: Matteo Croce <teknoraver@meta.com>

Reviewed-by: Eric Dumazet <edumazet@google.com>