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From: Huang Jianan <huangjianan@oppo.com>
To: linux-unionfs@vger.kernel.org, miklos@szeredi.hu,
	linux-erofs@lists.ozlabs.org, xiang@kernel.org, chao@kernel.org
Cc: huangjianan@oppo.com, guoweichao@oppo.com, yh@oppo.com,
	zhangshiming@oppo.com, guanyuwei@oppo.com, jnhuang95@gmail.com,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH v3] ovl: fix null pointer when filesystem doesn't support direct IO
Date: Wed, 22 Sep 2021 15:23:26 +0800	[thread overview]
Message-ID: <20210922072326.3538-1-huangjianan@oppo.com> (raw)
In-Reply-To: <9ef909de-1854-b4be-d272-2b4cda52329f@oppo.com>

From: Huang Jianan <huangjianan@oppo.com>

At present, overlayfs provides overlayfs inode to users. Overlayfs
inode provides ovl_aops with noop_direct_IO to avoid open failure
with O_DIRECT. But some compressed filesystems, such as erofs and
squashfs, don't support direct_IO.

Users who use f_mapping->a_ops->direct_IO to check O_DIRECT support,
will read file through this way. This will cause overlayfs to access
a non-existent direct_IO function and cause panic due to null pointer:

Kernel panic - not syncing: CFI failure (target: 0x0)
CPU: 6 PID: 247 Comm: loop0
Call Trace:
 panic+0x188/0x45c
 __cfi_slowpath+0x0/0x254
 __cfi_slowpath+0x200/0x254
 generic_file_read_iter+0x14c/0x150
 vfs_iocb_iter_read+0xac/0x164
 ovl_read_iter+0x13c/0x2fc
 lo_rw_aio+0x2bc/0x458
 loop_queue_work+0x4a4/0xbc0
 kthread_worker_fn+0xf8/0x1d0
 loop_kthread_worker_fn+0x24/0x38
 kthread+0x29c/0x310
 ret_from_fork+0x10/0x30

The filesystem may only support direct_IO for some file types. For
example, erofs supports direct_IO for uncompressed files. So return
-EINVAL when the file doesn't support direct_IO to fix this problem.

Fixes: 5b910bd615ba ("ovl: fix GPF in swapfile_activate of file from overlayfs over xfs")
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
---
change since v2:
 - Return error in ovl_open directly. (Chengguang Xu)

Change since v1:
 - Return error to user rather than fall back to buffered io. (Chengguang Xu)

 fs/overlayfs/file.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index d081faa55e83..a0c99ea35daf 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -157,6 +157,10 @@ static int ovl_open(struct inode *inode, struct file *file)
 	if (IS_ERR(realfile))
 		return PTR_ERR(realfile);
 
+	if ((f->f_flags & O_DIRECT) && (!realfile->f_mapping->a_ops ||
+		!realfile->f_mapping->a_ops->direct_IO))
+		return -EINVAL;
+
 	file->private_data = realfile;
 
 	return 0;
-- 
2.25.1


  reply	other threads:[~2021-09-22  7:23 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-18 12:13 [PATCH] " Huang Jianan
2021-09-22  1:56 ` Chengguang Xu
2021-09-22  3:39   ` Huang Jianan
2021-09-22  3:47 ` [PATCH v2] " Huang Jianan
2021-09-22  5:09   ` Chengguang Xu
2021-09-22  7:18     ` Huang Jianan
2021-09-22  7:23       ` Huang Jianan [this message]
2021-09-22  8:06         ` [PATCH v3] " Chengguang Xu
2021-09-22  8:24           ` Huang Jianan
2021-09-22 13:20             ` [PATCH v3] ovl: fix null pointer when filesystemdoesn'tsupportdirect IO Chengguang Xu
2021-09-22 14:00               ` Miklos Szeredi
2021-09-27  9:38                 ` Miklos Szeredi
2021-09-28  7:01                   ` Huang Jianan
2021-09-28  7:17                     ` Miklos Szeredi

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