From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: [PATCH] IB/ucma: Fix theoretical user triggered use-after-free Date: Tue, 4 Aug 2015 17:13:32 -0600 Message-ID: <20150804231332.GA22959@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Sean Hefty Cc: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-rdma@vger.kernel.org Something like this: CPU A CPU B ======================== ================================ ucma_destroy_id() wait_for_completion() .. anything ucma_put_ctx() complete() .. continues ... ucma_leave_multicast() mutex_lock(mut) atomic_inc(ctx->ref) mutex_unlock(mut) ucma_free_ctx() ucma_cleanup_multicast() mutex_lock(mut) kfree(mc) rdma_leave_multicast(mc->ctx->cm_id,.. Fix it by latching the ref at 0. Once it goes to 0 mc and ctx cannot leave the mutex(mut) protection. The other atomic_inc in ucma_get_ctx is OK because mutex(mut) protects it from racing with ucma_destroy_id. Signed-off-by: Jason Gunthorpe --- drivers/infiniband/core/ucma.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c index 29b21213ea75..acac9eafdbf6 100644 --- a/drivers/infiniband/core/ucma.c +++ b/drivers/infiniband/core/ucma.c @@ -1321,10 +1321,10 @@ static ssize_t ucma_leave_multicast(struct ucma_file *file, mc = ERR_PTR(-ENOENT); else if (mc->ctx->file != file) mc = ERR_PTR(-EINVAL); - else { + else if (!atomic_inc_not_zero(&mc->ctx->ref)) + mc = ERR_PTR(-ENXIO); + else idr_remove(&multicast_idr, mc->id); - atomic_inc(&mc->ctx->ref); - } mutex_unlock(&mut); if (IS_ERR(mc)) { -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html