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From: Huang Jianan via Linux-erofs <>
Subject: [PATCH v2] ovl: fix null pointer when filesystem doesn't support direct IO
Date: Wed, 22 Sep 2021 11:47:00 +0800	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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:

The filesystem may only support direct_IO for some file types. For
example, erofs supports direct_IO for uncompressed files. So reset
f_mapping->a_ops to NULL 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 <>
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..38118d3b46f8 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))
+		file->f_mapping->a_ops = NULL;
 	file->private_data = realfile;
 	return 0;

  parent reply	other threads:[~2021-09-22  3:47 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-18 12:13 [PATCH] ovl: fix null pointer when filesystem doesn't support direct IO Huang Jianan via Linux-erofs
2021-09-22  1:56 ` Chengguang Xu
2021-09-22  3:39   ` Huang Jianan via Linux-erofs
2021-09-22  3:47 ` Huang Jianan via Linux-erofs [this message]
2021-09-22  5:09   ` [PATCH v2] " Chengguang Xu
2021-09-22  7:18     ` Huang Jianan via Linux-erofs
2021-09-22  7:23       ` [PATCH v3] " Huang Jianan via Linux-erofs
2021-09-22  8:06         ` Chengguang Xu
2021-09-22  8:24           ` Huang Jianan via Linux-erofs
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 via Linux-erofs
2021-09-28  7:17                     ` Miklos Szeredi

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