linux-kernel - [PATCH 1/1] autofs: dont trigger mount if it cant succeed

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20251118024631.10854-2-raven@themaw.net>
Date: Tue, 18 Nov 2025 10:46:31 +0800
From: Ian Kent <raven@...maw.net>
To: Christian Brauner <brauner@...nel.org>,
	Al Viro <viro@...IV.linux.org.uk>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	autofs mailing list <autofs@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Cc: Ian Kent <raven@...maw.net>
Subject: [PATCH 1/1] autofs: dont trigger mount if it cant succeed

If a mount namespace contains autofs mounts, and they are propagation
private, and there is no namespace specific automount daemon to handle
possible automounting then attempted path resolution will loop until
MAXSYMLINKS is reached before failing causing quite a bit of noise in
the log.

Add a check for this in autofs ->d_automount() so that the VFS can
immediately return an error in this case. Since the mount is propagation
private an EPERM return seems most appropriate.

Suggested by: Christian Brauner <brauner@...nel.org>
Signed-off-by: Ian Kent <raven@...maw.net>
---
 fs/autofs/autofs_i.h  | 5 +++++
 fs/autofs/dev-ioctl.c | 1 +
 fs/autofs/inode.c     | 1 +
 fs/autofs/root.c      | 8 ++++++++
 fs/namespace.c        | 6 ++++++
 include/linux/fs.h    | 1 +
 6 files changed, 22 insertions(+)

diff --git a/fs/autofs/autofs_i.h b/fs/autofs/autofs_i.h
index 23cea74f9933..4fd555528c5d 100644
--- a/fs/autofs/autofs_i.h
+++ b/fs/autofs/autofs_i.h
@@ -16,6 +16,7 @@
 #include <linux/wait.h>
 #include <linux/sched.h>
 #include <linux/sched/signal.h>
+#include <uapi/linux/mount.h>
 #include <linux/mount.h>
 #include <linux/namei.h>
 #include <linux/uaccess.h>
@@ -27,6 +28,9 @@
 #include <linux/magic.h>
 #include <linux/fs_context.h>
 #include <linux/fs_parser.h>
+#include "../mount.h"
+#include <linux/ns_common.h>
+
 
 /* This is the range of ioctl() numbers we claim as ours */
 #define AUTOFS_IOC_FIRST     AUTOFS_IOC_READY
@@ -114,6 +118,7 @@ struct autofs_sb_info {
 	int pipefd;
 	struct file *pipe;
 	struct pid *oz_pgrp;
+	u64 mnt_ns_id;
 	int version;
 	int sub_version;
 	int min_proto;
diff --git a/fs/autofs/dev-ioctl.c b/fs/autofs/dev-ioctl.c
index 8adef8caa863..6b9a6de1c6fb 100644
--- a/fs/autofs/dev-ioctl.c
+++ b/fs/autofs/dev-ioctl.c
@@ -381,6 +381,7 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
 		swap(sbi->oz_pgrp, new_pid);
 		sbi->pipefd = pipefd;
 		sbi->pipe = pipe;
+		sbi->mnt_ns_id = to_ns_common(current->nsproxy->mnt_ns)->ns_id;
 		sbi->flags &= ~AUTOFS_SBI_CATATONIC;
 	}
 out:
diff --git a/fs/autofs/inode.c b/fs/autofs/inode.c
index f5c16ffba013..732aee76a24c 100644
--- a/fs/autofs/inode.c
+++ b/fs/autofs/inode.c
@@ -251,6 +251,7 @@ static struct autofs_sb_info *autofs_alloc_sbi(void)
 	sbi->min_proto = AUTOFS_MIN_PROTO_VERSION;
 	sbi->max_proto = AUTOFS_MAX_PROTO_VERSION;
 	sbi->pipefd = -1;
+	sbi->mnt_ns_id = to_ns_common(current->nsproxy->mnt_ns)->ns_id;
 
 	set_autofs_type_indirect(&sbi->type);
 	mutex_init(&sbi->wq_mutex);
diff --git a/fs/autofs/root.c b/fs/autofs/root.c
index 174c7205fee4..d10df9d89d1c 100644
--- a/fs/autofs/root.c
+++ b/fs/autofs/root.c
@@ -341,6 +341,14 @@ static struct vfsmount *autofs_d_automount(struct path *path)
 	if (autofs_oz_mode(sbi))
 		return NULL;
 
+	/* Refuse to trigger mount if current namespace is not the owner
+	 * and the mount is propagation private.
+	 */
+	if (sbi->mnt_ns_id != to_ns_common(current->nsproxy->mnt_ns)->ns_id) {
+		if (vfsmount_to_propagation_flags(path->mnt) & MS_PRIVATE)
+			return ERR_PTR(-EPERM);
+	}
+
 	/*
 	 * If an expire request is pending everyone must wait.
 	 * If the expire fails we're still mounted so continue
diff --git a/fs/namespace.c b/fs/namespace.c
index 2bad25709b2c..786ac259c399 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -5141,6 +5141,12 @@ static u64 mnt_to_propagation_flags(struct mount *m)
 	return propagation;
 }
 
+u64 vfsmount_to_propagation_flags(struct vfsmount *mnt)
+{
+	return mnt_to_propagation_flags(real_mount(mnt));
+}
+EXPORT_SYMBOL_GPL(vfsmount_to_propagation_flags);
+
 static void statmount_sb_basic(struct kstatmount *s)
 {
 	struct super_block *sb = s->mnt->mnt_sb;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index dd3b57cfadee..d876ace737e1 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3271,6 +3271,7 @@ extern struct file * open_exec(const char *);
 /* fs/dcache.c -- generic fs support functions */
 extern bool is_subdir(struct dentry *, struct dentry *);
 extern bool path_is_under(const struct path *, const struct path *);
+u64 vfsmount_to_propagation_flags(struct vfsmount *mnt);
 
 extern char *file_path(struct file *, char *, int);
 
-- 
2.51.1