smb/client: mark missing nlink values as unknown

Several SMB1 fallback and open responses do not provide the hard link
count. The SMB2 create-only query fallback has the same limitation.
These paths currently leave a zero link count or synthesize a value of
one and then expose it as authoritative metadata.

Mark those results with unknown_nlink so existing inodes keep their
cached link count and new inodes receive the usual sane default.

This was tested against Samba with "server min protocol = NT1". Mount
the share using SMB1 with Unix extensions disabled:

  mount -t cifs //<server>/<share> /mnt/cifs \
        -o username=<user>,vers=1.0,nounix

Create three names for the same inode and cache its real link count:

  TESTDIR=/mnt/cifs/nlink-repro-$$
  mkdir "$TESTDIR"
  touch "$TESTDIR/file1"
  ln "$TESTDIR/file1" "$TESTDIR/file2"
  ln "$TESTDIR/file1" "$TESTDIR/file3"
  stat -c 'before open: %h' "$TESTDIR/file1"

Open the file and read the link count through the open descriptor:

  exec 3<"$TESTDIR/file1"
  stat -Lc 'after open: %h' /proc/$$/fd/3
  exec 3<&-

Clean up the test files:

  rm -f "$TESTDIR/file1" "$TESTDIR/file2" "$TESTDIR/file3"
  rmdir "$TESTDIR"

Before this change, the two stat commands report 3 and 1 because the
SMB1 open response overwrites the known link count. With this change,
both commands report 3.

Signed-off-by: Ze Tan <tanze@kylinos.cn>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>

2 files changed, 8 insertions, 1 deletions

diff --git a/fs/smb/client/smb1ops.c b/fs/smb/client/smb1ops.c
index dc5a8c1da623..7e2b29060f51 100644
--- a/fs/smb/client/smb1ops.c
+++ b/fs/smb/client/smb1ops.c
@@ -542,6 +542,7 @@ static int cifs_query_path_info(const unsigned int xid,
 
 	data->reparse_point = false;
 	data->adjust_tz = false;
+	data->unknown_nlink = false;
 
 	/*
 	 * First try CIFSSMBQPathInfo() function which returns more info
@@ -608,6 +609,7 @@ static int cifs_query_path_info(const unsigned int xid,
 				fi.EASize = di->EaSize;
 			}
 			fi.NumberOfLinks = cpu_to_le32(1);
+			data->unknown_nlink = true;
 			fi.DeletePending = 0;
 			fi.Directory = !!(le32_to_cpu(fi.Attributes) & ATTR_DIRECTORY);
 			cifs_buf_release(search_info.ntwrk_buf_start);
@@ -630,6 +632,8 @@ static int cifs_query_path_info(const unsigned int xid,
 		rc = SMBQueryInformation(xid, tcon, full_path, &fi, cifs_sb->local_nls,
 					 cifs_remap(cifs_sb));
 		data->adjust_tz = true;
+		if (!rc)
+			data->unknown_nlink = true;
 	} else if ((rc == -EOPNOTSUPP || rc == -EINVAL) && non_unicode_wildcard) {
 		/* Path with non-UNICODE wildcard character cannot exist. */
 		rc = -ENOENT;
@@ -893,8 +897,10 @@ static int cifs_open_file(const unsigned int xid, struct cifs_open_parms *oparms
 	else
 		rc = CIFS_open(xid, oparms, oplock, &fi);
 
-	if (!rc && data)
+	if (!rc && data) {
 		move_cifs_info_to_smb2(&data->fi, &fi);
+		data->unknown_nlink = true;
+	}
 
 	return rc;
 }
diff --git a/fs/smb/client/smb2inode.c b/fs/smb/client/smb2inode.c
index 213bc298cdf2..d4ae8a5ad463 100644
--- a/fs/smb/client/smb2inode.c
+++ b/fs/smb/client/smb2inode.c
@@ -576,6 +576,7 @@ finished:
 		idata->fi.EndOfFile = create_rsp->EndofFile;
 		if (le32_to_cpu(idata->fi.NumberOfLinks) == 0)
 			idata->fi.NumberOfLinks = cpu_to_le32(1); /* dummy value */
+		idata->unknown_nlink = true;
 		idata->fi.DeletePending = 0; /* successful open = not delete pending */
 		idata->fi.Directory = !!(le32_to_cpu(create_rsp->FileAttributes) & ATTR_DIRECTORY);