Re: [PATCH] ucma: fix a use-after-free in ucma_resolve_ip()

[Leon Romanovsky]

On Wed, Sep 12, 2018 at 04:27:44PM -0700, Cong Wang wrote:
> There is a race condition between ucma_close() and ucma_resolve_ip():
>
> CPU0				CPU1
> ucma_resolve_ip():		ucma_close():
>
> ctx = ucma_get_ctx(file, cmd.id);
>
>         list_for_each_entry_safe(ctx, tmp, &file->ctx_list, list) {
>                 mutex_lock(&mut);
>                 idr_remove(&ctx_idr, ctx->id);
>                 mutex_unlock(&mut);
> 		...
>                 mutex_lock(&mut);
>                 if (!ctx->closing) {
>                         mutex_unlock(&mut);
>                         rdma_destroy_id(ctx->cm_id);
> 		...
>                 ucma_free_ctx(ctx);
>
> ret = rdma_resolve_addr();
> ucma_put_ctx(ctx);
>
> Before idr_remove(), ucma_get_ctx() could still find the ctx
> and after rdma_destroy_id(), rdma_resolve_addr() may still
> access id_priv pointer. Also, ucma_put_ctx() may use ctx after
> ucma_free_ctx() too.
>
> ucma_close() should call ucma_put_ctx() too which tests the
> refcnt and waits for the last one releasing it. The similar
> pattern is already used by ucma_destroy_id().
>
> Reported-and-tested-by: syzbot+da2591e115d57a9cbb8b@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: syzbot+cfe3c1e8ef634ba8964b@xxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> Cc: Doug Ledford <dledford@xxxxxxxxxx>
> Cc: Leon Romanovsky <leon@xxxxxxxxxx>
> Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
> ---
>  drivers/infiniband/core/ucma.c | 2 ++
>  1 file changed, 2 insertions(+)
>

Thanks,
Reviewed-by: Leon Romanovsky <leonro@xxxxxxxxxxxx>

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