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From: Chen Hanxiao <chenhx.fnst@fujitsu.com>
To: jlayton@kernel.org
Cc: Dai.Ngo@oracle.com,
	chenhx.fnst@fujitsu.com,
	chuck.lever@oracle.com,
	kolga@netapp.com,
	linux-nfs@vger.kernel.org,
	neilb@suse.de,
	tom@talpey.com
Subject: Re: [PATCH] NFSD: nfsctl: remove read permission of filehandle
Date: Wed, 27 Mar 2024 14:40:00 +0800
Message-Id: <20240327064000.1363-1-chenhx.fnst@fujitsu.com>
In-Reply-To: <21f3580de20445ddd9bdae6eecc316a58b6df97d.camel@kernel.org>
References: <21f3580de20445ddd9bdae6eecc316a58b6df97d.camel@kernel.org>
Precedence: bulk
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Hi, Jeff

I wrote a POC patch, use name_to_handle_at to get nfs root filehandle
instead of /proc/fs/nfsd/filehandle.

I did some simple tests and it works.

Pls check the POC patch below:
---
 support/export/cache.c | 95 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 93 insertions(+), 2 deletions(-)

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
 
+#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;	/* == 1 */
+			uint8_t		fh_auth_type;	/* deprecated */
+			uint8_t		fh_fsid_type;
+			uint8_t		fh_fileid_type;
+			uint32_t	fh_fsid[]; /* flexible-array member */
+		};
+	};
+};
+
 enum nfsd_fsid {
 	FSID_DEV = 0,
 	FSID_NUM,
@@ -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, char *p)
 	return &fh;
 }
 
+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] = {0};
+	char *mesg = 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));
+	
+	file_fh.fh.handle_bytes = 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 = 1;
+	kfh.fh_auth_type = 0;
+	e_fsid = exp->m_export.e_fsid;
+
+	if (e_fsid > 0) {
+		len = 12;
+		fh.fh_size = 8;
+		kfh.fh_size = 12;
+		kfh.fh_fsid_type = 1;
+		kfh.fh_fsid[0] = e_fsid;
+	} else {
+		len = file_fh.fh.handle_bytes + 8;
+		fh.fh_size = file_fh.fh.handle_bytes;
+		kfh.fh_size = file_fh.fh.handle_bytes + sizeof(kfh.fh_size);
+		kfh.fh_fsid_type = FSID_UUID16_INUM;
+		if (file_fh.fh.handle_bytes <= 12) {
+			kfh.fh_fsid[0] = *(uint32_t *)file_fh.fh.f_handle;
+			kfh.fh_fsid[1] = 0;
+		} else {
+			kfh.fh_fsid[0] = *(uint32_t *)file_fh.fh.f_handle;
+			kfh.fh_fsid[1] = *((uint32_t *)file_fh.fh.f_handle + 1);
+		}
+	}
+	kfh.fh_fileid_type = 0; // FILEID_ROOT
+
+	qword_addhex(&mesg, &len, kfh.fh_raw, kfh.fh_size);
+	mesg = buf;
+	len = qword_get(&mesg, (char *)fh.fh_handle, NFS3_FHSIZE);
+	if (e_fsid == 0) {
+		len = 16;
+		uuid_by_path(name, 0, 16, u);
+		memcpy((char *)fh.fh_handle+12, u, 16);
+		fh.fh_size += 16;
+	}
+	
+	return &fh;
+}
+
+struct nfs_fh_len *
+cache_get_filehandle(nfs_export *exp, int len, char *p)
+{
+	struct nfs_fh_len *fh;
+	fh = cache_get_filehandle_by_name(exp, p);
+	if (!fh)
+		fh = 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)
-- 
2.39.1