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Message-ID: <009e4477af2b6359c7e9bb549f0982a667c6ffa1.camel@kernel.org>
Subject: Re: [PATCH] NFSD: nfsctl: remove read permission of filehandle
From: Jeff Layton <jlayton@kernel.org>
To: Chen Hanxiao <chenhx.fnst@fujitsu.com>
Cc: Dai.Ngo@oracle.com, chuck.lever@oracle.com, kolga@netapp.com, 
	linux-nfs@vger.kernel.org, neilb@suse.de, tom@talpey.com
Date: Wed, 27 Mar 2024 06:50:37 -0400
In-Reply-To: <20240327064000.1363-1-chenhx.fnst@fujitsu.com>
References: <21f3580de20445ddd9bdae6eecc316a58b6df97d.camel@kernel.org>
	 <20240327064000.1363-1-chenhx.fnst@fujitsu.com>
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On Wed, 2024-03-27 at 14:40 +0800, Chen Hanxiao wrote:
> Hi, Jeff
>=20
> I wrote a POC patch, use name_to_handle_at to get nfs root filehandle
> instead of /proc/fs/nfsd/filehandle.
>=20
> I did some simple tests and it works.
>=20
> Pls check the POC patch below:
> ---
>  support/export/cache.c | 95 +++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 93 insertions(+), 2 deletions(-)
>=20

Very cool!

I do think this is the basic direction we want to go with revising how
mountd gets its filehandles.=20


> diff --git a/support/export/cache.c b/support/export/cache.c
> index 6c0a44a3..adecac2e 100644
> --- a/support/export/cache.c
> +++ b/support/export/cache.c
> @@ -43,6 +43,25 @@
>  #include "blkid/blkid.h"
>  #endif
> =20
> +#define NFS4_FHSIZE           128
> +
> +struct knfsd_fh {
> +	unsigned int	fh_size;	/*
> +					 * Points to the current size while
> +					 * building a new file handle.
> +					 */
> +	union {
> +		char			fh_raw[NFS4_FHSIZE];
> +		struct {
> +			uint8_t		fh_version;	/* =3D=3D 1 */
> +			uint8_t		fh_auth_type;	/* deprecated */
> +			uint8_t		fh_fsid_type;
> +			uint8_t		fh_fileid_type;
> +			uint32_t	fh_fsid[]; /* flexible-array member */
> +		};
> +	};
> +};
> +

This is a large departure from how this has worked in the past. Before
this, userland could always treat a knfsd_fh as opaque. With this change
though, knfsd_fh will need to be part of the kernel's ABI, and we'll
need to be very careful about future changes to the FH format (not that
we're planning any).

I think we probably ought to start by moving the definitions of knfsd_fh
and its component parts into a UAPI header that nfs-utils could then
use. For now, we can add duplicate definitions like above for when the
case where they aren't defined in UAPI headers.

>  enum nfsd_fsid {
>  	FSID_DEV =3D 0,
>  	FSID_NUM,

Side note: I wonder if some of the nfsd_fsid values can (effectively) be
deprecated these days? I don't think we really use FSID_DEV anymore at
all, do we?

> @@ -1827,8 +1846,8 @@ int cache_export(nfs_export *exp, char *path)
>   *   read filehandle <&0
>   * } <> /proc/fs/nfsd/filehandle
>   */
> -struct nfs_fh_len *
> -cache_get_filehandle(nfs_export *exp, int len, char *p)
> +static struct nfs_fh_len *
> +cache_get_filehandle_by_proc(nfs_export *exp, int len, char *p)
>  {
>  	static struct nfs_fh_len fh;
>  	char buf[RPC_CHAN_BUF_SIZE], *bp;
> @@ -1862,6 +1881,78 @@ cache_get_filehandle(nfs_export *exp, int len, cha=
r *p)
>  	return &fh;
>  }
> =20
> +static struct nfs_fh_len *
> +cache_get_filehandle_by_name(nfs_export *exp, char *name)
> +{
> +	static struct nfs_fh_len fh;
> +	struct {
> +		struct file_handle fh;
> +		unsigned char handle[128];
> +	} file_fh;
> +	char buf[RPC_CHAN_BUF_SIZE] =3D {0};
> +	char *mesg =3D buf;
> +	int len, mnt_id;
> +	unsigned int e_fsid;
> +	struct knfsd_fh kfh;
> +	char u[16];
> +
> +	memset(fh.fh_handle, 0, sizeof(fh.fh_handle));
> +=09
> +	file_fh.fh.handle_bytes =3D 128;
> +	if (name_to_handle_at(AT_FDCWD, name, &file_fh.fh, &mnt_id, 0) < 0)
> +		return NULL;
> +
> +	memset(fh.fh_handle, 0, sizeof(fh.fh_handle));
> +	memset(&kfh, 0, sizeof(struct knfsd_fh));
> +	kfh.fh_version =3D 1;
> +	kfh.fh_auth_type =3D 0;
> +	e_fsid =3D exp->m_export.e_fsid;
> +
> +	if (e_fsid > 0) {
> +		len =3D 12;
> +		fh.fh_size =3D 8;
> +		kfh.fh_size =3D 12;
> +		kfh.fh_fsid_type =3D 1;
> +		kfh.fh_fsid[0] =3D e_fsid;
> +	} else {
> +		len =3D file_fh.fh.handle_bytes + 8;
> +		fh.fh_size =3D file_fh.fh.handle_bytes;
> +		kfh.fh_size =3D file_fh.fh.handle_bytes + sizeof(kfh.fh_size);
> +		kfh.fh_fsid_type =3D FSID_UUID16_INUM;

Note that we will need to deal with NFSv2 here too. It has 32-byte
filehandles, and so we likely can't use FSID_UUID16_INUM for those.

> +		if (file_fh.fh.handle_bytes <=3D 12) {
> +			kfh.fh_fsid[0] =3D *(uint32_t *)file_fh.fh.f_handle;
> +			kfh.fh_fsid[1] =3D 0;
> +		} else {
> +			kfh.fh_fsid[0] =3D *(uint32_t *)file_fh.fh.f_handle;
> +			kfh.fh_fsid[1] =3D *((uint32_t *)file_fh.fh.f_handle + 1);
> +		}
> +	}
> +	kfh.fh_fileid_type =3D 0; // FILEID_ROOT
> +
> +	qword_addhex(&mesg, &len, kfh.fh_raw, kfh.fh_size);
> +	mesg =3D buf;
> +	len =3D qword_get(&mesg, (char *)fh.fh_handle, NFS3_FHSIZE);

We may need to pass to this function what version of NFS MNT request was
sent so that we know what sort of FH is needed here.

> +	if (e_fsid =3D=3D 0) {
> +		len =3D 16;
> +		uuid_by_path(name, 0, 16, u);
> +		memcpy((char *)fh.fh_handle+12, u, 16);
> +		fh.fh_size +=3D 16;
> +	}
> +=09
> +	return &fh;
> +}
> +
> +struct nfs_fh_len *
> +cache_get_filehandle(nfs_export *exp, int len, char *p)
> +{
> +	struct nfs_fh_len *fh;
> +	fh =3D cache_get_filehandle_by_name(exp, p);
> +	if (!fh)
> +		fh =3D cache_get_filehandle_by_proc(exp, len, p);
> +
> +	return fh;
> +}
> +
>  /* Wait for all worker child processes to exit and reap them */
>  void
>  cache_wait_for_workers(char *prog)

This looks like a great start -- nice work! There are a number of more
obscure corner-cases that we'll need to deal with, but this does look
like a promising direction.
--=20
Jeff Layton <jlayton@kernel.org>