On Thu, Jun 11, 2020 at 12:45:03PM +1000, Dave Chinner wrote:
>
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> xlog_wait() on the CIL context can reference a freed context if the
> waiter doesn't get scheduled before the CIL context is freed. This
> can happen when a task is on the hard throttle and the CIL push
> aborts due to a shutdown. This was detected by generic/019:
>
> thread 1 thread 2
>
> __xfs_trans_commit
> xfs_log_commit_cil
> <CIL size over hard throttle limit>
> xlog_wait
> schedule
> xlog_cil_push_work
> wake_up_all
> <shutdown aborts commit>
> xlog_cil_committed
> kmem_free
>
> remove_wait_queue
> spin_lock_irqsave --> UAF
>
> Fix it by moving the wait queue to the CIL rather than keeping it in
> in the CIL context that gets freed on push completion. Because the
> wait queue is now independent of the CIL context and we might have
> multiple contexts in flight at once, only wake the waiters on the
> push throttle when the context we are pushing is over the hard
> throttle size threshold.
>
> Fixes: 0e7ab7efe7745 ("xfs: Throttle commits on delayed background CIL push")
> Reported-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
Looks reasonable:
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> fs/xfs/xfs_log_cil.c | 10 +++++-----
> fs/xfs/xfs_log_priv.h | 2 +-
> 2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index b43f0e8f43f2e..9ed90368ab311 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -671,7 +671,8 @@ xlog_cil_push_work(
> /*
> * Wake up any background push waiters now this context is being pushed.
> */
> - wake_up_all(&ctx->push_wait);
> + if (ctx->space_used >= XLOG_CIL_BLOCKING_SPACE_LIMIT(log))
> + wake_up_all(&cil->xc_push_wait);
>
> /*
> * Check if we've anything to push. If there is nothing, then we don't
> @@ -743,13 +744,12 @@ xlog_cil_push_work(
>
> /*
> * initialise the new context and attach it to the CIL. Then attach
> - * the current context to the CIL committing lsit so it can be found
> + * the current context to the CIL committing list so it can be found
> * during log forces to extract the commit lsn of the sequence that
> * needs to be forced.
> */
> INIT_LIST_HEAD(&new_ctx->committing);
> INIT_LIST_HEAD(&new_ctx->busy_extents);
> - init_waitqueue_head(&new_ctx->push_wait);
> new_ctx->sequence = ctx->sequence + 1;
> new_ctx->cil = cil;
> cil->xc_ctx = new_ctx;
> @@ -937,7 +937,7 @@ xlog_cil_push_background(
> if (cil->xc_ctx->space_used >= XLOG_CIL_BLOCKING_SPACE_LIMIT(log)) {
> trace_xfs_log_cil_wait(log, cil->xc_ctx->ticket);
> ASSERT(cil->xc_ctx->space_used < log->l_logsize);
> - xlog_wait(&cil->xc_ctx->push_wait, &cil->xc_push_lock);
> + xlog_wait(&cil->xc_push_wait, &cil->xc_push_lock);
> return;
> }
>
> @@ -1216,12 +1216,12 @@ xlog_cil_init(
> INIT_LIST_HEAD(&cil->xc_committing);
> spin_lock_init(&cil->xc_cil_lock);
> spin_lock_init(&cil->xc_push_lock);
> + init_waitqueue_head(&cil->xc_push_wait);
> init_rwsem(&cil->xc_ctx_lock);
> init_waitqueue_head(&cil->xc_commit_wait);
>
> INIT_LIST_HEAD(&ctx->committing);
> INIT_LIST_HEAD(&ctx->busy_extents);
> - init_waitqueue_head(&ctx->push_wait);
> ctx->sequence = 1;
> ctx->cil = cil;
> cil->xc_ctx = ctx;
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index ec22c7a3867f1..75a62870b63af 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -240,7 +240,6 @@ struct xfs_cil_ctx {
> struct xfs_log_vec *lv_chain; /* logvecs being pushed */
> struct list_head iclog_entry;
> struct list_head committing; /* ctx committing list */
> - wait_queue_head_t push_wait; /* background push throttle */
> struct work_struct discard_endio_work;
> };
>
> @@ -274,6 +273,7 @@ struct xfs_cil {
> wait_queue_head_t xc_commit_wait;
> xfs_lsn_t xc_current_sequence;
> struct work_struct xc_push_work;
> + wait_queue_head_t xc_push_wait; /* background push throttle */
> } ____cacheline_aligned_in_smp;
>
> /*
>
