smb: client: fix missing timestamp updates after utime(2)

Don't reuse open handle when changing timestamps to prevent the server
from disabling automatic timestamp updates as per MS-FSA 2.1.4.17.

---8<---
import os
import time

filename = '/mnt/foo'

def print_stat(prefix):
    st = os.stat(filename)
    print(prefix, ': ', time.ctime(st.st_atime), time.ctime(st.st_ctime))

fd = os.open(filename, os.O_CREAT|os.O_TRUNC|os.O_WRONLY, 0o644)
print_stat('old')
os.utime(fd, None)
time.sleep(2)
os.write(fd, b'foo')
os.close(fd)
time.sleep(2)
print_stat('new')
---8<---

Before patch:

$ mount.cifs //srv/share /mnt -o ...
$ python3 run.py
old :  Fri Oct  3 14:01:21 2025 Fri Oct  3 14:01:21 2025
new :  Fri Oct  3 14:01:21 2025 Fri Oct  3 14:01:21 2025

After patch:

$ mount.cifs //srv/share /mnt -o ...
$ python3 run.py
old :  Fri Oct  3 17:03:34 2025 Fri Oct  3 17:03:34 2025
new :  Fri Oct  3 17:03:36 2025 Fri Oct  3 17:03:36 2025

Fixes: b6f2a0f ("cifs: for compound requests, use open handle if possible")
Signed-off-by: Paulo Alcantara (Red Hat) <[email protected]>
Cc: Frank Sorenson <[email protected]>
Reviewed-by: David Howells <[email protected]>
Cc: [email protected]
Signed-off-by: Steve French <[email protected]>

Author: pcacjr

fs/smb/client/smb2inode.c

@@ -1382,31 +1382,33 @@ int
 smb2_set_file_info(struct inode *inode, const char *full_path,
 		   FILE_BASIC_INFO *buf, const unsigned int xid)
 {
-	struct cifs_open_parms oparms;
+	struct kvec in_iov = { .iov_base = buf, .iov_len = sizeof(*buf), };
 	struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);
+	struct cifsFileInfo *cfile = NULL;
+	struct cifs_open_parms oparms;
 	struct tcon_link *tlink;
 	struct cifs_tcon *tcon;
-	struct cifsFileInfo *cfile;
-	struct kvec in_iov = { .iov_base = buf, .iov_len = sizeof(*buf), };
-	int rc;
-
-	if ((buf->CreationTime == 0) && (buf->LastAccessTime == 0) &&
-	    (buf->LastWriteTime == 0) && (buf->ChangeTime == 0) &&
-	    (buf->Attributes == 0))
-		return 0; /* would be a no op, no sense sending this */
+	int rc = 0;
 
 	tlink = cifs_sb_tlink(cifs_sb);
 	if (IS_ERR(tlink))
 		return PTR_ERR(tlink);
 	tcon = tlink_tcon(tlink);
 
-	cifs_get_writable_path(tcon, full_path, FIND_WR_ANY, &cfile);
+	if ((buf->CreationTime == 0) && (buf->LastAccessTime == 0) &&
+	    (buf->LastWriteTime == 0) && (buf->ChangeTime == 0)) {
+		if (buf->Attributes == 0)
+			goto out; /* would be a no op, no sense sending this */
+		cifs_get_writable_path(tcon, full_path, FIND_WR_ANY, &cfile);
+	}
+
 	oparms = CIFS_OPARMS(cifs_sb, tcon, full_path, FILE_WRITE_ATTRIBUTES,
 			     FILE_OPEN, 0, ACL_NO_MODE);
 	rc = smb2_compound_op(xid, tcon, cifs_sb,
 			      full_path, &oparms, &in_iov,
 			      &(int){SMB2_OP_SET_INFO}, 1,
 			      cfile, NULL, NULL, NULL);
+out:
 	cifs_put_tlink(tlink);
 	return rc;
 }