From: ChenXiaoSong <chenxiaosong2@huawei.com>
Date: Tue, 29 Mar 2022 19:32:08 +0800
Subject: [PATCH] NFSv4: fix open failure with O_ACCMODE flag
Git-commit: b243874f6f9568b2daf1a00e9222cacdc15e159c
Patch-mainline: v5.18
References: git-fixes

open() with O_ACCMODE|O_DIRECT flags secondly will fail.

Reproducer: 1. mount -t nfs -o vers=4.2 $server_ip:/ /mnt/
  2. fd = open("/mnt/file", O_ACCMODE|O_DIRECT|O_CREAT)
  3. close(fd)
  4. fd = open("/mnt/file", O_ACCMODE|O_DIRECT)

Server nfsd4_decode_share_access() will fail with error nfserr_bad_xdr when
client use incorrect share access mode of 0.

Fix this by using NFS4_SHARE_ACCESS_BOTH share access mode in client,
just like firstly opening.

Fixes: ce4ef7c0a8a05 ("NFS: Split out NFS v4 file operations")
Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/nfs/dir.c      |   10 ----------
 fs/nfs/internal.h |   10 ++++++++++
 fs/nfs/nfs4file.c |    6 ++++--
 3 files changed, 14 insertions(+), 12 deletions(-)

--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1501,16 +1501,6 @@ const struct dentry_operations nfs4_dent
 };
 EXPORT_SYMBOL_GPL(nfs4_dentry_operations);
 
-static fmode_t flags_to_mode(int flags)
-{
-	fmode_t res = (__force fmode_t)flags & FMODE_EXEC;
-	if ((flags & O_ACCMODE) != O_WRONLY)
-		res |= FMODE_READ;
-	if ((flags & O_ACCMODE) != O_RDONLY)
-		res |= FMODE_WRITE;
-	return res;
-}
-
 static struct nfs_open_context *create_nfs_open_context(struct dentry *dentry, int open_flags, struct file *filp)
 {
 	return alloc_nfs_open_context(dentry, flags_to_mode(open_flags), filp);
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -48,6 +48,16 @@ struct nfs_clone_mount {
 	rpc_authflavor_t authflavor;
 };
 
+static inline fmode_t flags_to_mode(int flags)
+{
+	fmode_t res = (__force fmode_t)flags & FMODE_EXEC;
+	if ((flags & O_ACCMODE) != O_WRONLY)
+		res |= FMODE_READ;
+	if ((flags & O_ACCMODE) != O_RDONLY)
+		res |= FMODE_WRITE;
+	return res;
+}
+
 /*
  * Note: RFC 1813 doesn't limit the number of auth flavors that
  * a server can return, so make something up.
--- a/fs/nfs/nfs4file.c
+++ b/fs/nfs/nfs4file.c
@@ -30,6 +30,7 @@ nfs4_file_open(struct inode *inode, stru
 	struct dentry *parent = NULL;
 	struct inode *dir;
 	unsigned openflags = filp->f_flags;
+	fmode_t f_mode;
 	struct iattr attr;
 	int err;
 
@@ -48,8 +49,9 @@ nfs4_file_open(struct inode *inode, stru
 	if (err)
 		return err;
 
+	f_mode = filp->f_mode;
 	if ((openflags & O_ACCMODE) == 3)
-		openflags--;
+		f_mode |= flags_to_mode(openflags);
 
 	/* We can't create new files here */
 	openflags &= ~(O_CREAT|O_EXCL);
@@ -57,7 +59,7 @@ nfs4_file_open(struct inode *inode, stru
 	parent = dget_parent(dentry);
 	dir = d_inode(parent);
 
-	ctx = alloc_nfs_open_context(file_dentry(filp), filp->f_mode, filp);
+	ctx = alloc_nfs_open_context(file_dentry(filp), f_mode, filp);
 	err = PTR_ERR(ctx);
 	if (IS_ERR(ctx))
 		goto out;