[PATCH v7 2/5] proc: subset=pid: Show /proc/self/net only for CAP_NET_ADMIN

Alexey Gladkov
2026-01-13T09:21:18Z

Cache the mounters credentials and allow access to the net directories
contingent of the permissions of the mounter of proc.

Do not show /proc/self/net when proc is mounted with subset=pid option
and the mounter does not have CAP_NET_ADMIN.

Signed-off-by: Alexey Gladkov <legion@kernel.org>
---
fs/proc/proc_net.c | 8 ++++++++
fs/proc/root.c | 5 +++++
include/linux/proc_fs.h | 1 +
3 files changed, 14 insertions(+)

diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index 52f0b75cbce2..6e0ccef0169f 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -23,6 +23,7 @@
#include <linux/uidgid.h>
#include <net/net_namespace.h>
#include <linux/seq_file.h>
+#include <linux/security.h>

#include "internal.h"

@@ -270,6 +271,7 @@ static struct net *get_proc_task_net(struct inode *dir)
struct task_struct *task;
struct nsproxy *ns;
struct net *net = NULL;
+ struct proc_fs_info *fs_info = proc_sb_info(dir->i_sb);

rcu_read_lock();
task = pid_task(proc_pid(dir), PIDTYPE_PID);
@@ -282,6 +284,12 @@ static struct net *get_proc_task_net(struct inode *dir)
}
rcu_read_unlock();

+ if (net && (fs_info->pidonly == PROC_PIDONLY_ON) &&
+ security_capable(fs_info->mounter_cred, net->user_ns, CAP_NET_ADMIN, CAP_OPT_NONE) < 0) {
+ put_net(net);
+ net = NULL;
+ }
+
return net;
}

diff --git a/fs/proc/root.c b/fs/proc/root.c
index d8ca41d823e4..ed8a101d09d3 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -254,6 +254,7 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
return -ENOMEM;

fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
+ fs_info->mounter_cred = get_cred(fc->cred);
proc_apply_options(fs_info, fc, current_user_ns());

/* User space would break if executables or devices appear on proc */
@@ -303,6 +304,9 @@ static int proc_reconfigure(struct fs_context *fc)

sync_filesystem(sb);

+ put_cred(fs_info->mounter_cred);
+ fs_info->mounter_cred = get_cred(fc->cred);
+
proc_apply_options(fs_info, fc, current_user_ns());
return 0;
}
@@ -350,6 +354,7 @@ static void proc_kill_sb(struct super_block *sb)
kill_anon_super(sb);
if (fs_info) {
put_pid_ns(fs_info->pid_ns);
+ put_cred(fs_info->mounter_cred);
kfree_rcu(fs_info, rcu);
}
}
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 19d1c5e5f335..ec123c277d49 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -67,6 +67,7 @@ enum proc_pidonly {
struct proc_fs_info {
struct pid_namespace *pid_ns;
kgid_t pid_gid;
+ const struct cred *mounter_cred;
enum proc_hidepid hide_pid;
enum proc_pidonly pidonly;
struct rcu_head rcu;
--
2.52.0