On Mon, Nov 07, 2022 at 10:27:15PM +0800, Guo Xuenan wrote:
> Fix uaf in xfs_trans_ail_delete during xlog force shutdown.
> In commit cd6f79d1fb32 ("xfs: run callbacks before waking waiters in
> xlog_state_shutdown_callbacks") changed the order of running callbacks
> and wait for iclog completion to avoid unmount path untimely destroy AIL.
> But which seems not enough to ensue this, adding mdelay in
> `xfs_buf_item_unpin` can prove that.
>
> The reproduction is as follows. To ensure destroy AIL safely,
> we should wait all xlog ioend workers done and sync the AIL.
>
> ==================================================================
> BUG: KASAN: use-after-free in xfs_trans_ail_delete+0x240/0x2a0
> Read of size 8 at addr ffff888023169400 by task kworker/1:1H/43
>
> CPU: 1 PID: 43 Comm: kworker/1:1H Tainted: G W
> 6.1.0-rc1-00002-gc28266863c4a #137
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> 1.13.0-1ubuntu1.1 04/01/2014
> Workqueue: xfs-log/sda xlog_ioend_work
> Call Trace:
> <TASK>
> dump_stack_lvl+0x4d/0x66
> print_report+0x171/0x4a6
> kasan_report+0xb3/0x130
> xfs_trans_ail_delete+0x240/0x2a0
> xfs_buf_item_done+0x7b/0xa0
> xfs_buf_ioend+0x1e9/0x11f0
> xfs_buf_item_unpin+0x4c8/0x860
> xfs_trans_committed_bulk+0x4c2/0x7c0
> xlog_cil_committed+0xab6/0xfb0
> xlog_cil_process_committed+0x117/0x1e0
> xlog_state_shutdown_callbacks+0x208/0x440
> xlog_force_shutdown+0x1b3/0x3a0
> xlog_ioend_work+0xef/0x1d0
> process_one_work+0x6f9/0xf70
> worker_thread+0x578/0xf30
> kthread+0x28c/0x330
> ret_from_fork+0x1f/0x30
> </TASK>
>
> Allocated by task 9606:
> kasan_save_stack+0x1e/0x40
> kasan_set_track+0x21/0x30
> __kasan_kmalloc+0x7a/0x90
> __kmalloc+0x59/0x140
> kmem_alloc+0xb2/0x2f0
> xfs_trans_ail_init+0x20/0x320
> xfs_log_mount+0x37e/0x690
> xfs_mountfs+0xe36/0x1b40
> xfs_fs_fill_super+0xc5c/0x1a70
> get_tree_bdev+0x3c5/0x6c0
> vfs_get_tree+0x85/0x250
> path_mount+0xec3/0x1830
> do_mount+0xef/0x110
> __x64_sys_mount+0x150/0x1f0
> do_syscall_64+0x35/0x80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> Freed by task 9662:
> kasan_save_stack+0x1e/0x40
> kasan_set_track+0x21/0x30
> kasan_save_free_info+0x2a/0x40
> __kasan_slab_free+0x105/0x1a0
> __kmem_cache_free+0x99/0x2d0
> kvfree+0x3a/0x40
> xfs_log_unmount+0x60/0xf0
> xfs_unmountfs+0xf3/0x1d0
> xfs_fs_put_super+0x78/0x300
> generic_shutdown_super+0x151/0x400
> kill_block_super+0x9a/0xe0
> deactivate_locked_super+0x82/0xe0
> deactivate_super+0x91/0xb0
> cleanup_mnt+0x32a/0x4a0
> task_work_run+0x15f/0x240
> exit_to_user_mode_prepare+0x188/0x190
> syscall_exit_to_user_mode+0x12/0x30
> do_syscall_64+0x42/0x80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> The buggy address belongs to the object at ffff888023169400
> which belongs to the cache kmalloc-128 of size 128
> The buggy address is located 0 bytes inside of
> 128-byte region [ffff888023169400, ffff888023169480)
>
> The buggy address belongs to the physical page:
> page:ffffea00008c5a00 refcount:1 mapcount:0 mapping:0000000000000000
> index:0xffff888023168f80 pfn:0x23168
> head:ffffea00008c5a00 order:1 compound_mapcount:0 compound_pincount:0
> flags: 0x1fffff80010200(slab|head|node=0|zone=1|lastcpupid=0x1fffff)
> raw: 001fffff80010200 ffffea00006b3988 ffffea0000577a88 ffff88800f842ac0
> raw: ffff888023168f80 0000000000150007 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ffff888023169300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff888023169380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >ffff888023169400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> ffff888023169480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff888023169500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
> Disabling lock debugging due to kernel taint
>
> Fixes: cd6f79d1fb32 ("xfs: run callbacks before waking waiters in xlog_state_shutdown_callbacks")
> Signed-off-by: Guo Xuenan <guoxuenan@xxxxxxxxxx>
> ---
> fs/xfs/xfs_log.c | 33 ++++++++++++++++++++++-----------
> 1 file changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index f02a0dd522b3..89fcd2b8cdfc 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -82,6 +82,9 @@ STATIC int
> xlog_iclogs_empty(
> struct xlog *log);
>
> +static void
> +xlog_wait_iodone(struct xlog *log);
> +
> static int
> xfs_log_cover(struct xfs_mount *);
>
> @@ -886,6 +889,23 @@ xlog_force_iclog(
> return xlog_state_release_iclog(iclog->ic_log, iclog, NULL);
> }
>
> +/*
> + * Cycle all the iclogbuf locks to make sure all log IO completion
> + * is done before we tear down AIL/CIL.
> + */
> +static void
> +xlog_wait_iodone(struct xlog *log)
It's ok to have pulled this into a helper function, but to repeat a
question from v1: why shouldn't this be done as part of xfs_log_quiesce?
Is there a particular reason why we *don't* want to wait for log IO
completions as part of a freeze? I guess that's because a frozen dead
filesystem still has all the incore state, so log IO completion work
racing with the freeze isn't a big deal?
> +{
> + int i;
> + xlog_in_core_t *iclog = log->l_iclog;
Nit: Please use 'struct xlog_in_core', not the typedefs.
> +
> + for (i = 0; i < log->l_iclog_bufs; i++) {
> + down(&iclog->ic_sema);
> + up(&iclog->ic_sema);
> + iclog = iclog->ic_next;
> + }
> +}
> +
> /*
> * Wait for the iclog and all prior iclogs to be written disk as required by the
> * log force state machine. Waiting on ic_force_wait ensures iclog completions
> @@ -1095,6 +1115,7 @@ xfs_log_clean(
> struct xfs_mount *mp)
> {
> xfs_log_quiesce(mp);
> + xlog_wait_iodone(mp->m_log);
Wherever you inject this callsite, it needs a comment stating /why/ it's
necessary to wait for the iclog completions even after a log force and
xfs_ail_push_all_sync call.
--D
> xfs_log_unmount_write(mp);
> }
>
> @@ -2113,17 +2134,7 @@ xlog_dealloc_log(
> xlog_in_core_t *iclog, *next_iclog;
> int i;
>
> - /*
> - * Cycle all the iclogbuf locks to make sure all log IO completion
> - * is done before we tear down these buffers.
> - */
> - iclog = log->l_iclog;
> - for (i = 0; i < log->l_iclog_bufs; i++) {
> - down(&iclog->ic_sema);
> - up(&iclog->ic_sema);
> - iclog = iclog->ic_next;
> - }
> -
> + xlog_wait_iodone(log);
> /*
> * Destroy the CIL after waiting for iclog IO completion because an
> * iclog EIO error will try to shut down the log, which accesses the
> --
> 2.31.1
>
