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proc: subset=pid: Show /proc/self/net only for CAP_NET_ADMIN

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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. To avoid inadvertently
allowing access to /proc/<pid>/net, updating mounter credentials is not
supported.

Signed-off-by: Alexey Gladkov <legion@kernel.org>
Link: https://patch.msgid.link/d2466fe9085367f1e24693c437ecb8cff2789660.1777278334.git.legion@kernel.org
Reviewed-by: Aleksa Sarai <aleksa@amutable.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Alexey Gladkov 2026-04-27 10:26:05 +02:00 committed by Christian Brauner
parent 78d797520f
commit a2a5eb6323
3 changed files with 11 additions and 0 deletions
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8
fs/proc/proc_net.c
View File

@ -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;
}

2
fs/proc/root.c
View File

@ -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 */
@ -350,6 +351,7 @@ 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);
}
}

1
include/linux/proc_fs.h
View File

@ -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;