在 2021/9/22 16:24, Huang Jianan 写道:
在 2021/9/22 16:06, Chengguang Xu 写道:
在 2021/9/22 15:23, Huang Jianan 写道:
From: Huang Jianan <huangjianan@xxxxxxxx>
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:
I just looked around the code more closely, in open_with_fake_path(),
do_dentry_open() has already checked O_DIRECT open flag and
a_ops->direct_IO of underlying real address_space.
Am I missing something?
It seems that loop_update_dio will set lo->use_dio after open file
without set O_DIRECT.
loop_update_dio will check f_mapping->a_ops->direct_IO but it deal
with ovl_aops with
noop _direct_IO.
So I think we still need a new aops?
It means we should only set ->direct_IO for overlayfs inodes whose
underlying fs has DIRECT IO ability.
Hi Miklos,
Is it right solution for this kind of issue? What do you think?
Thanks,
Chengguang
Thanks,
Jianan
Thanks,
Chengguang
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@xxxxxxxx>
---
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;
