linux-kernel - [PATCH 3/4] ovl: restrict to exportable file handles

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Message-ID: <20241201-work-exportfs-v1-3-b850dda4502a@kernel.org>
Date: Sun,  1 Dec 2024 14:12:27 +0100
From: Christian Brauner <brauner@...nel.org>
To: Amir Goldstein <amir73il@...il.com>,
	Jeff Layton <jlayton@...nel.org>
Cc: Christian Brauner <brauner@...nel.org>,
	Erin Shepherd <erin.shepherd@....eu>,
	Chuck Lever <chuck.lever@...cle.com>,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-nfs@...r.kernel.org
Subject: [PATCH 3/4] ovl: restrict to exportable file handles

Ensure that overlayfs only allows decoding exportable file handles.

Signed-off-by: Christian Brauner <brauner@...nel.org>
---
 fs/overlayfs/util.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 9aa7493b1e10365cbcc97fceab26d614a319727f..b498c74084f3950d8e4d9f63a804d1abe08258fc 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -83,10 +83,15 @@ void ovl_revert_creds(const struct cred *old_cred)
  */
 int ovl_can_decode_fh(struct super_block *sb)
 {
+	const struct export_operations *nop = sb->s_export_op;
+
 	if (!capable(CAP_DAC_READ_SEARCH))
 		return 0;
 
-	if (!exportfs_can_decode_fh(sb->s_export_op))
+	if (!exportfs_can_decode_fh(nop))
+		return 0;
+
+	if (nop && nop->flags & EXPORT_OP_LOCAL_FILE_HANDLE)
 		return 0;
 
 	return sb->s_export_op->encode_fh ? -1 : FILEID_INO32_GEN;

-- 
2.45.2