Re: [PATCH 2/2] autofs: dont trigger mount if it cant succeed

[Christian Brauner <brauner@kernel.org>]

On Tue, Nov 11, 2025 at 02:04:39PM +0800, Ian Kent wrote:
> 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.
> 
> Signed-off-by: Ian Kent <raven@themaw.net>
> ---
>  fs/autofs/autofs_i.h | 4 ++++
>  fs/autofs/inode.c    | 1 +
>  fs/autofs/root.c     | 8 ++++++++
>  fs/namespace.c       | 6 ++++++
>  include/linux/fs.h   | 1 +
>  5 files changed, 20 insertions(+)
> 
> diff --git a/fs/autofs/autofs_i.h b/fs/autofs/autofs_i.h
> index 23cea74f9933..34533587c66b 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>
> @@ -109,11 +110,14 @@ struct autofs_wait_queue {
>  #define AUTOFS_SBI_STRICTEXPIRE 0x0002
>  #define AUTOFS_SBI_IGNORE	0x0004
>  
> +struct mnt_namespace;
> +
>  struct autofs_sb_info {
>  	u32 magic;
>  	int pipefd;
>  	struct file *pipe;
>  	struct pid *oz_pgrp;
> +	struct mnt_namespace *owner;
>  	int version;
>  	int sub_version;
>  	int min_proto;
> diff --git a/fs/autofs/inode.c b/fs/autofs/inode.c
> index f5c16ffba013..0a29761f39c0 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->owner = current->nsproxy->mnt_ns;

ns_ref_get()
Can be called directly on the mount namespace.