Re: [PATCH v3] ovl: fix null pointer when filesystem doesn't support direct IO
From: Chengguang Xu <hidden>
Date: 2021-09-22 08:06:36
Also in:
linux-fsdevel, lkml
在 2021/9/22 15:23, Huang Jianan 写道:
From: Huang Jianan <redacted> 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? Thanks, Chengguang
quoted hunk ↗ jump to hunk
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 <redacted> --- 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;