9p: check memory allocation result for cachetag

Check memory allocation result for cachetag in mount option parsing and
fix potential memory leak in the error case.

Link: http://lkml.kernel.org/r/1521614889-73446-1-git-send-email-cgxu519@gmx.comSigned-off-by: Chengguang Xu <cgxu519@gmx.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: <v9fs-developer@lists.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/9p/v9fs.c

@@ -292,6 +292,10 @@ static int v9fs_parse_options(struct v9fs_session_info *v9ses, char *opts)
 #ifdef CONFIG_9P_FSCACHE
 			kfree(v9ses->cachetag);
 			v9ses->cachetag = match_strdup(&args[0]);
+			if (!v9ses->cachetag) {
+				ret = -ENOMEM;
+				goto free_and_return;
+			}
 #endif
 			break;
 		case Opt_cache:
@@ -471,6 +475,9 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
 	return fid;
 
 err_clnt:
+#ifdef CONFIG_9P_FSCACHE
+	kfree(v9ses->cachetag);
+#endif
 	p9_client_destroy(v9ses->clnt);
 err_names:
 	kfree(v9ses->uname);