linux-kernel - [PATCH v1 2/2] Show /proc/self/net only for CAP_NET

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Message-Id: <20200727141411.203770-3-gladkov.alexey@gmail.com>
Date:   Mon, 27 Jul 2020 16:14:11 +0200
From:   Alexey Gladkov <gladkov.alexey@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Gladkov <legion@...nel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>
Subject: [PATCH v1 2/2] Show /proc/self/net only for CAP_NET_ADMIN

Show /proc/self/net only for CAP_NET_ADMIN if procfs is mounted with
subset=pid option in user namespace. This is done to avoid possible
information leakage.

Signed-off-by: Alexey Gladkov <gladkov.alexey@...il.com>
---
 fs/proc/proc_net.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index dba63b2429f0..11fa2c4b3529 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -275,6 +275,12 @@ 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);
+
+	if ((fs_info->pidonly == PROC_PIDONLY_ON) &&
+	    (current_user_ns() != &init_user_ns) &&
+	    !capable(CAP_NET_ADMIN))
+		return net;
 
 	rcu_read_lock();
 	task = pid_task(proc_pid(dir), PIDTYPE_PID);
-- 
2.25.4