[PATCH AUTOSEL 5.4 2/2] smb3: do not error on fsync when readonly

[Sasha Levin <sashal@kernel.org>]

From: Steve French <stfrench@microsoft.com>

[ Upstream commit 71e6864eacbef0b2645ca043cdfbac272cb6cea3 ]

Linux allows doing a flush/fsync on a file open for read-only,
but the protocol does not allow that.  If the file passed in
on the flush is read-only try to find a writeable handle for
the same inode, if that is not possible skip sending the
fsync call to the server to avoid breaking the apps.

Reported-by: Julian Sikorski <belegdol@gmail.com>
Tested-by: Julian Sikorski <belegdol@gmail.com>
Suggested-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/cifs/file.c | 35 +++++++++++++++++++++++++++++------
 1 file changed, 29 insertions(+), 6 deletions(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index a9746af5a44db..03c85beecec10 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2577,12 +2577,23 @@ int cifs_strict_fsync(struct file *file, loff_t start, loff_t end,
 	tcon = tlink_tcon(smbfile->tlink);
 	if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NOSSYNC)) {
 		server = tcon->ses->server;
-		if (server->ops->flush)
-			rc = server->ops->flush(xid, tcon, &smbfile->fid);
-		else
+		if (server->ops->flush == NULL) {
 			rc = -ENOSYS;
+			goto strict_fsync_exit;
+		}
+
+		if ((OPEN_FMODE(smbfile->f_flags) & FMODE_WRITE) == 0) {
+			smbfile = find_writable_file(CIFS_I(inode), FIND_WR_ANY);
+			if (smbfile) {
+				rc = server->ops->flush(xid, tcon, &smbfile->fid);
+				cifsFileInfo_put(smbfile);
+			} else
+				cifs_dbg(FYI, "ignore fsync for file not open for write\n");
+		} else
+			rc = server->ops->flush(xid, tcon, &smbfile->fid);
 	}
 
+strict_fsync_exit:
 	free_xid(xid);
 	return rc;
 }
@@ -2594,6 +2605,7 @@ int cifs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	struct cifs_tcon *tcon;
 	struct TCP_Server_Info *server;
 	struct cifsFileInfo *smbfile = file->private_data;
+	struct inode *inode = file_inode(file);
 	struct cifs_sb_info *cifs_sb = CIFS_FILE_SB(file);
 
 	rc = file_write_and_wait_range(file, start, end);
@@ -2608,12 +2620,23 @@ int cifs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	tcon = tlink_tcon(smbfile->tlink);
 	if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NOSSYNC)) {
 		server = tcon->ses->server;
-		if (server->ops->flush)
-			rc = server->ops->flush(xid, tcon, &smbfile->fid);
-		else
+		if (server->ops->flush == NULL) {
 			rc = -ENOSYS;
+			goto fsync_exit;
+		}
+
+		if ((OPEN_FMODE(smbfile->f_flags) & FMODE_WRITE) == 0) {
+			smbfile = find_writable_file(CIFS_I(inode), FIND_WR_ANY);
+			if (smbfile) {
+				rc = server->ops->flush(xid, tcon, &smbfile->fid);
+				cifsFileInfo_put(smbfile);
+			} else
+				cifs_dbg(FYI, "ignore fsync for file not open for write\n");
+		} else
+			rc = server->ops->flush(xid, tcon, &smbfile->fid);
 	}
 
+fsync_exit:
 	free_xid(xid);
 	return rc;
 }
-- 
2.33.0