cifs: prevent use-after-free by freeing the cfile later

In smb2_compound_op we have a possible use-after-free
which can cause hard to debug problems later on.

This was revealed during stress testing with KASAN enabled
kernel. Fixing it by moving the cfile free call to
a few lines below, after the usage.

Fixes: 76894f3 ("cifs: improve symlink handling for smb2+")
Reviewed-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: sprasad-microsoft

fs/smb/client/smb2inode.c

@@ -398,9 +398,6 @@ static int smb2_compound_op(const unsigned int xid, struct cifs_tcon *tcon,
 					rsp_iov);
 
  finished:
-	if (cfile)
-		cifsFileInfo_put(cfile);
-
 	SMB2_open_free(&rqst[0]);
 	if (rc == -EREMCHG) {
 		pr_warn_once("server share %s deleted\n", tcon->tree_name);
@@ -529,6 +526,9 @@ static int smb2_compound_op(const unsigned int xid, struct cifs_tcon *tcon,
 		break;
 	}
 
+	if (cfile)
+		cifsFileInfo_put(cfile);
+
 	if (rc && err_iov && err_buftype) {
 		memcpy(err_iov, rsp_iov, 3 * sizeof(*err_iov));
 		memcpy(err_buftype, resp_buftype, 3 * sizeof(*err_buftype));