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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. > Agreed, I will send v2 to fix it. Thanks, Jianan > > Thanks, > > Chengguang > > >> >> Fixes: 5b910bd615ba ("ovl: fix GPF in swapfile_activate of file from >> overlayfs over xfs") >> Signed-off-by: Huang Jianan >> --- >> 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, >