From patchwork Mon Apr 19 12:36:31 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Palash Oswal X-Patchwork-Id: 12211771 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 712F3C433B4 for ; Mon, 19 Apr 2021 12:48:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 49ACC6108B for ; Mon, 19 Apr 2021 12:48:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239223AbhDSMtX (ORCPT ); Mon, 19 Apr 2021 08:49:23 -0400 Received: from us2-ob2-7.mailhostbox.com ([208.91.199.208]:35224 "EHLO us2-ob2-7.mailhostbox.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232709AbhDSMtX (ORCPT ); Mon, 19 Apr 2021 08:49:23 -0400 X-Greylist: delayed 610 seconds by postgrey-1.27 at vger.kernel.org; Mon, 19 Apr 2021 08:49:23 EDT Received: from smtp.oswalpalash.com (unknown [49.36.79.38]) (Authenticated sender: hello@oswalpalash.com) by us2.outbound.mailhostbox.com (Postfix) with ESMTPA id 95FBC78261C; Mon, 19 Apr 2021 12:38:39 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oswalpalash.com; s=20160715; t=1618835922; bh=kT29ypuv7A855UVCqwpU0b49/ZfU+kqo9AeK/OVIgUE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=EpviTtNh58mftTBiwOb64P4RptPndOhK0W0A6d9nW0z0h8TFf1pMvQawvCXc8Y8zQ rBZuWS8LCZC+u77COSNtdAjOOPrRe7jpgOAYKrB2idOkdxS/o9KWAgQAbjde9AByx7 fpQIZ3ZNLNm1EJWt7zsCbWzJosmi2FQpgzf4XQeo= From: Palash Oswal To: Jens Axboe , Pavel Begunkov , Alexander Viro , io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Palash Oswal Subject: [PATCH] io_uring: check ctx->sq_data before io_sq_offload_start Date: Mon, 19 Apr 2021 18:06:31 +0530 Message-Id: <20210419123630.62212-1-hello@oswalpalash.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: https://lore.kernel.org/io-uring/d346085f-8b9b-d620-1e0c-aa78fee8db13@gmail.com References: MIME-Version: 1.0 X-CMAE-Score: 0 X-CMAE-Analysis: v=2.3 cv=I7wbu+og c=1 sm=1 tr=0 a=cdGxx36Ay0PF3zJPwW0H8g==:117 a=cdGxx36Ay0PF3zJPwW0H8g==:17 a=1WgTlICyNIAsNvkEdfwA:9 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org syzkaller identified KASAN: null-ptr-deref Read in io_uring_create bug on the stable 5.11-y tree. BUG: KASAN: null-ptr-deref in io_sq_offload_start fs/io_uring.c:8254 [inline] BUG: KASAN: null-ptr-deref in io_disable_sqo_submit fs/io_uring.c:8999 [inline] BUG: KASAN: null-ptr-deref in io_uring_create+0x1275/0x22f0 fs/io_uring.c:9824 Read of size 8 at addr 0000000000000068 by task syz-executor.0/4350 A simple reproducer for this bug is: int main(void) { syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 0ul); intptr_t res = 0; pid_t parent = getpid(); *(uint32_t*)0x20000084 = 0; *(uint32_t*)0x20000088 = 0x42; *(uint32_t*)0x2000008c = 0; *(uint32_t*)0x20000090 = 0; *(uint32_t*)0x20000098 = -1; *(uint32_t*)0x2000009c = 0; *(uint32_t*)0x200000a0 = 0; *(uint32_t*)0x200000a4 = 0; if (fork() == 0) { kill(parent,SIGKILL); exit(0); } res = syscall(__NR_io_uring_setup, 0x7994, 0x20000080ul); return 0; } Due to the SIGKILL sent to the process before io_uring_setup completes, ctx->sq_data is NULL. Therefore, io_sq_offload_start does a null pointer dereferenced read. More details on this bug are in [1]. Discussion for this patch happened in [2]. [1] https://oswalpalash.com/exploring-null-ptr-deref-io-uring-submit [2] https://lore.kernel.org/io-uring/a08121be-f481-e9f8-b28d-3eb5d4f a5b76@gmail.com/ Signed-off-by: Palash Oswal --- fs/io_uring.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) base-commit: 2aa8861eab092599ad566c5b20d7452d9ec0ca8e diff --git a/fs/io_uring.c b/fs/io_uring.c index 95b4a89dad4e..82a89ff315a4 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -8995,7 +8995,7 @@ static void io_disable_sqo_submit(struct io_ring_ctx *ctx) { mutex_lock(&ctx->uring_lock); ctx->sqo_dead = 1; - if (ctx->flags & IORING_SETUP_R_DISABLED) + if (ctx->flags & IORING_SETUP_R_DISABLED && ctx->sq_data) io_sq_offload_start(ctx); mutex_unlock(&ctx->uring_lock);