cifs: We do not drop reference to tlink in CIFSCheckMFSymlink()

When we obtain tcon from cifs_sb, we use cifs_sb_tlink() to first obtain
tlink which also grabs a reference to it. We do not drop this reference
to tlink once we are done with the call.

The patch fixes this issue by instead passing tcon as a parameter and
avoids having to obtain a reference to the tlink. A lookup for the tcon
is already made in the calling functions and this way we avoid having to
re-run the lookup. This is also consistent with the argument list for
other similar calls for M-F symlinks.

We should also return an ENOSYS when we do not find a protocol specific
function to lookup the MF Symlink data.

Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
CC: Stable <stable@kernel.org>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/cifsproto.h

@@ -477,9 +477,10 @@ extern int CIFSGetExtAttr(const unsigned int xid, struct cifs_tcon *tcon,
 			const int netfid, __u64 *pExtAttrBits, __u64 *pMask);
 extern void cifs_autodisable_serverino(struct cifs_sb_info *cifs_sb);
 extern bool CIFSCouldBeMFSymlink(const struct cifs_fattr *fattr);
-extern int CIFSCheckMFSymlink(struct cifs_fattr *fattr,
-		const unsigned char *path,
-		struct cifs_sb_info *cifs_sb, unsigned int xid);
+extern int CIFSCheckMFSymlink(unsigned int xid, struct cifs_tcon *tcon,
+			      struct cifs_sb_info *cifs_sb,
+			      struct cifs_fattr *fattr,
+			      const unsigned char *path);
 extern int mdfour(unsigned char *, unsigned char *, int);
 extern int E_md4hash(const unsigned char *passwd, unsigned char *p16,
 			const struct nls_table *codepage);

fs/cifs/inode.c

@@ -383,7 +383,8 @@ int cifs_get_inode_info_unix(struct inode **pinode,
 
 	/* check for Minshall+French symlinks */
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MF_SYMLINKS) {
-		int tmprc = CIFSCheckMFSymlink(&fattr, full_path, cifs_sb, xid);
+		int tmprc = CIFSCheckMFSymlink(xid, tcon, cifs_sb, &fattr,
+					       full_path);
 		if (tmprc)
 			cifs_dbg(FYI, "CIFSCheckMFSymlink: %d\n", tmprc);
 	}
@@ -799,7 +800,8 @@ cifs_get_inode_info(struct inode **inode, const char *full_path,
 
 	/* check for Minshall+French symlinks */
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MF_SYMLINKS) {
-		tmprc = CIFSCheckMFSymlink(&fattr, full_path, cifs_sb, xid);
+		tmprc = CIFSCheckMFSymlink(xid, tcon, cifs_sb, &fattr,
+					   full_path);
 		if (tmprc)
 			cifs_dbg(FYI, "CIFSCheckMFSymlink: %d\n", tmprc);
 	}

fs/cifs/link.c

@@ -354,34 +354,30 @@ open_query_close_cifs_symlink(const unsigned char *path, char *pbuf,
 
 
 int
-CIFSCheckMFSymlink(struct cifs_fattr *fattr,
-		   const unsigned char *path,
-		   struct cifs_sb_info *cifs_sb, unsigned int xid)
+CIFSCheckMFSymlink(unsigned int xid, struct cifs_tcon *tcon,
+		   struct cifs_sb_info *cifs_sb, struct cifs_fattr *fattr,
+		   const unsigned char *path)
 {
-	int rc = 0;
+	int rc;
 	u8 *buf = NULL;
 	unsigned int link_len = 0;
 	unsigned int bytes_read = 0;
-	struct cifs_tcon *ptcon;
 
 	if (!CIFSCouldBeMFSymlink(fattr))
 		/* it's not a symlink */
 		return 0;
 
 	buf = kmalloc(CIFS_MF_SYMLINK_FILE_SIZE, GFP_KERNEL);
-	if (!buf) {
-		rc = -ENOMEM;
-		goto out;
-	}
+	if (!buf)
+		return -ENOMEM;
 
-	ptcon = tlink_tcon(cifs_sb_tlink(cifs_sb));
-	if ((ptcon->ses) && (ptcon->ses->server->ops->query_mf_symlink))
-		rc = ptcon->ses->server->ops->query_mf_symlink(path, buf,
+	if (tcon->ses->server->ops->query_mf_symlink)
+		rc = tcon->ses->server->ops->query_mf_symlink(path, buf,
 						&bytes_read, cifs_sb, xid);
 	else
-		goto out;
+		rc = -ENOSYS;
 
-	if (rc != 0)
+	if (rc)
 		goto out;
 
 	if (bytes_read == 0) /* not a symlink */