[PATCH -next 2/2] NFSv4: fix open failure with O_ACCMODE flag

[ChenXiaoSong <chenxiaosong2@xxxxxxxxxx>]

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

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 75cb1cbe4cde..911bdb35eb08 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1853,16 +1853,6 @@ const struct dentry_operations nfs4_dentry_operations = {
 };
 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);
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index 2de7c56a1fbe..58e618a5d88e 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -42,6 +42,16 @@ static inline bool nfs_lookup_is_soft_revalidate(const struct dentry *dentry)
 	return true;
 }
 
+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.
diff --git a/fs/nfs/nfs4file.c b/fs/nfs/nfs4file.c
index c178db86a6e8..e34af48fb4f4 100644
--- a/fs/nfs/nfs4file.c
+++ b/fs/nfs/nfs4file.c
@@ -32,6 +32,7 @@ nfs4_file_open(struct inode *inode, struct file *filp)
 	struct dentry *parent = NULL;
 	struct inode *dir;
 	unsigned openflags = filp->f_flags;
+	fmode_t f_mode;
 	struct iattr attr;
 	int err;
 
@@ -50,8 +51,9 @@ nfs4_file_open(struct inode *inode, struct file *filp)
 	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);
@@ -59,7 +61,7 @@ nfs4_file_open(struct inode *inode, struct file *filp)
 	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;
-- 
2.31.1