linux-kernel - [PATCH v2 06/10] cachefiles, erofs: Fix NULL deref in when cachefiles is not doing ondemand-mode

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Date: Mon, 22 Jan 2024 22:32:19 +0000
From: David Howells <dhowells@...hat.com>
To: Christian Brauner <christian@...uner.io>
Cc: David Howells <dhowells@...hat.com>,
	Jeff Layton <jlayton@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	netfs@...ts.linux.dev,
	linux-afs@...ts.infradead.org,
	linux-cifs@...r.kernel.org,
	linux-nfs@...r.kernel.org,
	ceph-devel@...r.kernel.org,
	v9fs@...ts.linux.dev,
	linux-erofs@...ts.ozlabs.org,
	linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Marc Dionne <marc.dionne@...istor.com>,
	Gao Xiang <xiang@...nel.org>,
	Chao Yu <chao@...nel.org>,
	Yue Hu <huyue2@...lpad.com>,
	Jeffle Xu <jefflexu@...ux.alibaba.com>
Subject: [PATCH v2 06/10] cachefiles, erofs: Fix NULL deref in when cachefiles is not doing ondemand-mode

cachefiles_ondemand_init_object() as called from cachefiles_open_file() and
cachefiles_create_tmpfile() does not check if object->ondemand is set
before dereferencing it, leading to an oops something like:

	RIP: 0010:cachefiles_ondemand_init_object+0x9/0x41
	...
	Call Trace:
	 <TASK>
	 cachefiles_open_file+0xc9/0x187
	 cachefiles_lookup_cookie+0x122/0x2be
	 fscache_cookie_state_machine+0xbe/0x32b
	 fscache_cookie_worker+0x1f/0x2d
	 process_one_work+0x136/0x208
	 process_scheduled_works+0x3a/0x41
	 worker_thread+0x1a2/0x1f6
	 kthread+0xca/0xd2
	 ret_from_fork+0x21/0x33

Fix this by making cachefiles_ondemand_init_object() return immediately if
cachefiles->ondemand is NULL.

Fixes: 3c5ecfe16e76 ("cachefiles: extract ondemand info field from cachefiles_object")
Reported-by: Marc Dionne <marc.dionne@...istor.com>
Signed-off-by: David Howells <dhowells@...hat.com>
cc: Gao Xiang <xiang@...nel.org>
cc: Chao Yu <chao@...nel.org>
cc: Yue Hu <huyue2@...lpad.com>
cc: Jeffle Xu <jefflexu@...ux.alibaba.com>
cc: linux-erofs@...ts.ozlabs.org
cc: netfs@...ts.linux.dev
cc: linux-fsdevel@...r.kernel.org
---

Notes:
    Changes
    =======
    ver #2)
     - Move check of object->ondemand into cachefiles_ondemand_init_object()

 fs/cachefiles/ondemand.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index 5fd74ec60bef..4ba42f1fa3b4 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -539,6 +539,9 @@ int cachefiles_ondemand_init_object(struct cachefiles_object *object)
 	struct fscache_volume *volume = object->volume->vcookie;
 	size_t volume_key_size, cookie_key_size, data_len;
 
+	if (!object->ondemand)
+		return 0;
+
 	/*
 	 * CacheFiles will firstly check the cache file under the root cache
 	 * directory. If the coherency check failed, it will fallback to