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SubjectRe: [RFC PATCH 16/35] ovl: readd lsattr/chattr support
On Thu, Apr 12, 2018 at 6:08 PM, Miklos Szeredi <mszeredi@redhat.com> wrote:
> Implement FS_IOC_GETFLAGS and FS_IOC_SETFLAGS.
>
> Needs vfs_ioctl() exported to modules.
>
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
> ---
> fs/internal.h | 1 -
> fs/ioctl.c | 1 +
> fs/overlayfs/file.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 2 ++
> 4 files changed, 62 insertions(+), 1 deletion(-)
>
> diff --git a/fs/internal.h b/fs/internal.h
> index 3319bf39e339..d5108d9c6a2f 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -176,7 +176,6 @@ extern const struct dentry_operations ns_dentry_operations;
> */
> extern int do_vfs_ioctl(struct file *file, unsigned int fd, unsigned int cmd,
> unsigned long arg);
> -extern long vfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
>
> /*
> * iomap support:
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 5ace7efb0d04..696f4c46a868 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -49,6 +49,7 @@ long vfs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> out:
> return error;
> }
> +EXPORT_SYMBOL(vfs_ioctl);
>
> static int ioctl_fibmap(struct file *filp, int __user *p)
> {
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 05e3e2f80b89..cc004ff1b05b 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -8,6 +8,7 @@
>
> #include <linux/cred.h>
> #include <linux/file.h>
> +#include <linux/mount.h>
> #include <linux/xattr.h>
> #include <linux/uio.h>
> #include "overlayfs.h"
> @@ -291,6 +292,63 @@ long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> return ret;
> }
>
> +static long ovl_real_ioctl(struct file *file, unsigned int cmd,
> + unsigned long arg)
> +{
> + struct fd real;
> + const struct cred *old_cred;
> + long ret;
> +
> + ret = ovl_real_file(file, &real);
> + if (ret)
> + return ret;
> +
> + old_cred = ovl_override_creds(file_inode(file)->i_sb);
> + ret = vfs_ioctl(real.file, cmd, arg);
> + revert_creds(old_cred);
> +
> + fdput(real);
> +
> + return ret;
> +}
> +
> +long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> +{
> + long ret;
> + struct inode *inode = file_inode(file);
> +
> + switch (cmd) {
> + case FS_IOC_GETFLAGS:
> + ret = ovl_real_ioctl(file, cmd, arg);
> + break;
> +
> + case FS_IOC_SETFLAGS:
> + if (!inode_owner_or_capable(inode))
> + return -EACCES;
> +
> + ret = mnt_want_write_file(file);
> + if (ret)
> + return ret;
> +
> + ret = ovl_copy_up(file_dentry(file));
> + if (!ret) {
> + ret = ovl_real_ioctl(file, cmd, arg);
> +
> + inode_lock(inode);
> + ovl_copyflags(ovl_inode_real(inode), inode);
> + inode_unlock(inode);
> + }
> +
> + mnt_drop_write_file(file);
> + break;
> +
> + default:
> + ret = -ENOTTY;

I am wondering out loud.
This is a change of behavior that fs specific ioctls cannot be executed
on overlay file - arguably a good change of behavior, but still a change
that applications may got dependent on.

Would it have been better to opt-in for this change by a more generic
config/mount options, for example "consistent_fd" , instead of
"copy_up_shared" and then we can choose whether or not to
pass though unknown ioctls to real file.

I know we removed the want_write_file() protection from VFS, but
still, pass through of ioctls was the legacy behavior. Thoughts?
I don't mind to wait and see if someone shouts.

Thanks,
Amir.

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