在 2021/9/18 20:13, 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: 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 fall back to buffered io only when the file doesn't support direct_IO to fix this problem.
IMO, return error to user seems better option than fall back to buffered io directly. Thanks, Chengguang
Fixes: 5b910bd615ba ("ovl: fix GPF in swapfile_activate of file from overlayfs over xfs") Signed-off-by: Huang Jianan <huangjianan@xxxxxxxx> --- fs/overlayfs/file.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c index d081faa55e83..998c60770b81 100644 --- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -296,6 +296,10 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter) if (ret) return ret;+ if ((iocb->ki_flags & IOCB_DIRECT) && (!real.file->f_mapping->a_ops ||+ !real.file->f_mapping->a_ops->direct_IO)) + iocb->ki_flags &= ~IOCB_DIRECT; + old_cred = ovl_override_creds(file_inode(file)->i_sb); if (is_sync_kiocb(iocb)) { ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,
