On Mon, 1 Nov 2021 at 05:02, yangerkun <yangerkun@xxxxxxxxxx> wrote:
>
>
>
> On 2021/10/29 19:40, Miklos Szeredi wrote:
> > On Thu, Oct 28, 2021 at 08:41:28PM +0800, yangerkun wrote:
> >>
> >>
> >> 在 2021/10/18 22:26, yangerkun 写道:
> >>>
> >>>
> >>> 在 2021/10/8 23:13, Miklos Szeredi 写道:
> >>>> On Thu, 30 Sept 2021 at 05:12, yangerkun <yangerkun@xxxxxxxxxx> wrote:
> >>>>>
> >>>>> Our testcase trigger follow UAF:
> >>>>>
> >>>>> [ 153.939147]
> >>>>> ==================================================================
> >>>>> [ 153.942199] BUG: KASAN: use-after-free in
> >>>>> ext4_dio_read_iter+0xcc/0x1a0
> >>>>> [ 153.943331] Read of size 8 at addr ffff88803b7f1500 by task
> >>>>> fsstress/726
> >>>>> [ 153.948182] Call Trace:
> >>>>> [ 153.948628] ? dump_stack_lvl+0x73/0x9f
> >>>>> [ 153.950255] ? ext4_dio_read_iter+0xcc/0x1a0
> >>>>> [ 153.950972] ? ext4_dio_read_iter+0xcc/0x1a0
> >>>>> [ 153.951693] ? kasan_report.cold+0x81/0x165
> >>>>> [ 153.952429] ? ext4_dio_read_iter+0xcc/0x1a0
> >>>>> [ 153.953190] ? __asan_load8+0x74/0x110
> >>>>> [ 153.953856] ? ext4_dio_read_iter+0xcc/0x1a0
> >>>>> [ 153.954612] ? ext4_file_read_iter+0x1df/0x2a0
> >>>>> [ 153.955394] ? ext4_dio_read_iter+0x1a0/0x1a0
> >>>>> [ 153.956159] ? vfs_iocb_iter_read+0xd5/0x330
> >>>>> [ 153.956916] ? ovl_read_iter+0x15f/0x270
> >>>>> [ 153.957605] ? ovl_aio_cleanup_handler+0x2a0/0x2a0
> >>>>> [ 153.958436] ? aio_setup_rw+0xbf/0xe0
> >>>>> [ 153.959101] ? aio_read+0x190/0x2d0
> >>>>> [ 153.959750] ? aio_write+0x3e0/0x3e0
> >>>>> [ 153.960404] ? __kasan_check_read+0x1d/0x30
> >>>>> [ 153.961167] ? ext4_file_getattr+0x116/0x1b0
> >>>>> [ 153.961978] ? __put_user_ns+0x40/0x40
> >>>>> [ 153.962714] ? kasan_poison+0x40/0x90
> >>>>> [ 153.963384] ? set_alloc_info+0x46/0x70
> >>>>> [ 153.964102] ? __kasan_check_write+0x20/0x30
> >>>>> [ 153.964856] ? __fget_files+0x106/0x180
> >>>>> [ 153.965571] ? io_submit_one+0xaa7/0x1480
> >>>>> [ 153.966325] ? aio_poll_complete_work+0x590/0x590
> >>>>> [ 153.967713] ? ioctl_file_clone+0x110/0x110
> >>>>> [ 153.969008] ? vfs_getattr_nosec+0x14a/0x190
> >>>>> [ 153.970539] ? __do_sys_newfstat+0xd6/0xf0
> >>>>> [ 153.971713] ? __ia32_compat_sys_newfstat+0x40/0x40
> >>>>> [ 153.973005] ? __x64_sys_io_submit+0x125/0x3b0
> >>>>> [ 153.974282] ? __ia32_sys_io_submit+0x390/0x390
> >>>>> [ 153.975575] ? __kasan_check_read+0x1d/0x30
> >>>>> [ 153.976749] ? do_syscall_64+0x35/0x80
> >>>>> [ 153.978034] ? entry_SYSCALL_64_after_hwframe+0x44/0xae
> >>>>> [ 153.979436]
> >>>>> [ 153.979738] Allocated by task 726:
> >>>>> [ 153.980352] kasan_save_stack+0x23/0x60
> >>>>> [ 153.981054] set_alloc_info+0x46/0x70
> >>>>> [ 153.981745] __kasan_slab_alloc+0x4c/0x90
> >>>>> [ 153.982492] kmem_cache_alloc+0x153/0x750
> >>>>> [ 153.983953] ovl_read_iter+0x13b/0x270
> >>>>> [ 153.984689] aio_read+0x190/0x2d0
> >>>>> [ 153.985332] io_submit_one+0xaa7/0x1480
> >>>>> [ 153.986060] __x64_sys_io_submit+0x125/0x3b0
> >>>>> [ 153.986878] do_syscall_64+0x35/0x80
> >>>>> [ 153.987590] entry_SYSCALL_64_after_hwframe+0x44/0xae
> >>>>> [ 153.988516]
> >>>>> [ 153.988824] Freed by task 750:
> >>>>> [ 153.989417] kasan_save_stack+0x23/0x60
> >>>>> [ 153.990140] kasan_set_track+0x24/0x40
> >>>>> [ 153.990871] kasan_set_free_info+0x30/0x60
> >>>>> [ 153.991639] __kasan_slab_free+0x137/0x210
> >>>>> [ 153.992390] kmem_cache_free+0xf8/0x590
> >>>>> [ 153.993303] ovl_aio_cleanup_handler+0x1ae/0x2a0
> >>>>> [ 153.994205] ovl_aio_rw_complete+0x31/0x60
> >>>>> [ 153.995043] iomap_dio_complete_work+0x4b/0x60
> >>>>> [ 153.995898] iomap_dio_bio_end_io+0x23d/0x270
> >>>>> [ 153.996742] bio_endio+0x40d/0x440
> >>>>> [ 153.997376] blk_update_request+0x38f/0x820
> >>>>> [ 153.998160] scsi_end_request+0x56/0x320
> >>>>> [ 153.998872] scsi_io_completion+0x10a/0xb60
> >>>>> [ 153.999655] scsi_finish_command+0x194/0x2b0
> >>>>> [ 154.000464] scsi_complete+0xd7/0x1f0
> >>>>> [ 154.001184] blk_complete_reqs+0x92/0xb0
> >>>>> [ 154.001930] blk_done_softirq+0x29/0x40
> >>>>> [ 154.002696] __do_softirq+0x133/0x57f
> >>>>>
> >>>>> ext4_dio_read_iter
> >>>>> ret = iomap_dio_rw(iocb, to, &ext4_iomap_ops, NULL, 0)
> >>>>> file_accessed(iocb->ki_filp) <== this trigger UAF
> >>>>>
> >>>>> Ret can be -EIOCBQUEUED which means we will not wait for io
> >>>>> completion in
> >>>>> iomap_dio_rw. So the release for ovl_aio_req will be done when io
> >>>>> completion routine call ovl_aio_rw_complete(or ovl_aio_cleanup_handler
> >>>>> in ovl_read_iter will do this). But once io finish soon, we may already
> >>>>> release ovl_aio_req before we call file_access in ext4_dio_read_iter.
> >>>>> This can trigger the upper UAF.
> >>>>>
> >>>>> Fix it by introduce refcount in ovl_aio_req like what aio_kiocb has did.
> >>>>
> >>>> Looks good at a glance. Will review more fully.
> >>>
> >>> Hi,
> >>>
> >>> Any comments for this patch? :)
> >
> > Thanks for the patch. I found one issue: the fdput() needs to be moved to the
> > destruction as well, since the iocb->ki_filp reference comes from aio_req->fd.
>
> Hi, it seems we will only use aio_req->iocb in ovl_aio_cleanup_handler
> before we call fdput(aio_req->fd):
Correct. However I'm taking about this call:
file_accessed(iocb->ki_filp). If the fdput() is done from
ovl_aio_cleanup_handler() which is called from ->ki_complete() then
this would put the file, agains resulting in a UAF, only inside
file_accessed() this time. The reason why you weren't seeing this,
is probably that most of the time aio_req->fd is from
file->private_data, which is the real file obtained at open time, and
which isn't actually closed at fdput() (flags == 0).
>
> static void ovl_aio_cleanup_handler(struct ovl_aio_req *aio_req)
> {
> struct kiocb *iocb = &aio_req->iocb;
> struct kiocb *orig_iocb = aio_req->orig_iocb;
>
> if (iocb->ki_flags & IOCB_WRITE) {
> struct inode *inode = file_inode(orig_iocb->ki_filp);
>
> /* Actually acquired in ovl_write_iter() */
> __sb_writers_acquired(file_inode(iocb->ki_filp)->i_sb,
> SB_FREEZE_WRITE);
> file_end_write(iocb->ki_filp);
> <=== use iocb
> ovl_copyattr(ovl_inode_real(inode), inode);
> }
>
> orig_iocb->ki_pos = iocb->ki_pos;
> fdput(aio_req->fd); <=== release aio_req->fd
> kmem_cache_free(ovl_aio_request_cachep, aio_req);
> }
>
> So call fdput(aio_req->fd) in ovl_aio_cleanup_handler or ovl_aio_put
> seems all ok for me.
>
> >
> > Other than that, it looks good.
> >
> > Minor things:
> >
> > - instead of setting refcount to 1 and incrementing it, just initialize it to 2
> >
> > - code deduplication can come after the fix (if at all), this helps backporting
>
> Agree.
>
> >
> > - cleaned up header comment
> >
> > Here's the updated patch, can you please verify that I didn't break anything?
>
> Thanks! This patch can help pass the test!
Great, thanks.
Miklos
