| Message ID | 20210922034700.15666-1-huangjianan@oppo.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] ovl: fix null pointer when filesystem doesn't support direct IO | expand |
在 2021/9/22 11:47, Huang Jianan 写道: > 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 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 <huangjianan@oppo.com> > --- > 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; There are many other functions in a_ops and also address_space struct will be shared between files which belong to same inode. Although overlayfs currently only defines ->direct_IO in a_ops, it will be extended in the future. (like containerized sycnfs [1]) It seems the simplest solution is directly return error to upper layer. Thanks, Chengguang [1] https://www.spinics.net/lists/linux-unionfs/msg08569.html > + > file->private_data = realfile; > > return 0;
在 2021/9/22 13:09, Chengguang Xu 写道: > 在 2021/9/22 11:47, Huang Jianan 写道: >> 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 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 <huangjianan@oppo.com> >> --- >> 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; > > > There are many other functions in a_ops and also address_space struct > will be shared > > between files which belong to same inode. Although overlayfs currently > only defines > > ->direct_IO in a_ops, it will be extended in the future. (like > containerized sycnfs [1]) > > > It seems the simplest solution is directly return error to upper layer. > I think that after reset a_ops, do_dentry_open will check f_mapping->a_ops->direct_IO and return error. But return error directly in ovl_open seems to be a better solution, and won't affect future extend of ovl_aops. Thanks for pointing this out. Thanks, Jianan > > Thanks, > > Chengguang > > > [1] > https://apc01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.spinics.net%2Flists%2Flinux-unionfs%2Fmsg08569.html&data=04%7C01%7Chuangjianan%40oppo.com%7Ce01c8bb9ad4e4ac2670008d97d87321c%7Cf1905eb1c35341c5951662b4a54b5ee6%7C0%7C0%7C637678842352759179%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=Wo2uMfbYhqDOzDPSwHci2AVtM9y9nNstmayb741gspQ%3D&reserved=0 > > > >> + >> file->private_data = realfile; >> return 0; >
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;
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 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 <huangjianan@oppo.com> --- 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(+)