From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6657DC4167D for ; Tue, 7 Nov 2023 23:28:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344447AbjKGX2K (ORCPT ); Tue, 7 Nov 2023 18:28:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47398 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344526AbjKGX1v (ORCPT ); Tue, 7 Nov 2023 18:27:51 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E09B035B7; Tue, 7 Nov 2023 15:24:57 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 20546C433C9; Tue, 7 Nov 2023 23:24:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1699399497; bh=YoEAinzpXVzETYSEib6Djyp53Q1sMfVQG78G4mx3CXk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=hMWUpHC2D+cgp8mRVqflcWBIpa2aRSyngEzFftdLQd4cscVcDDClGRlPvEhf30WSM s4zwM91my0y49UNMLCF+JDiRQuHBgOIOImkKsr+9lqHILhy/Z2sO7YQYOCQrMcSbrh AVsrOznfWhsh6p1ZNjdoYMq0hI9Q+mC6mA9lZl06vSZRXFYW2CREpMEhfSm1Dgikcz +U8dh/6zVOEoQCak1EMYVMop0qhaBgeKCgNhu71pzHiXtNpDE8JDwjoTieHxAa49kU MAKagdmak5X6LVwYpdPQm0/6usSm0EyVOAMwsvY8VOtsiL//geMw+YyA38nKZ/Vqi+ MeBSxnNii1nXw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Marco Elver , syzbot+e441aeeb422763cc5511@syzkaller.appspotmail.com, Dominique Martinet , Sasha Levin , ericvh@kernel.org, lucho@ionkov.net, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, v9fs@lists.linux.dev, netdev@vger.kernel.org Subject: [PATCH AUTOSEL 5.15 5/6] 9p/trans_fd: Annotate data-racy writes to file::f_flags Date: Tue, 7 Nov 2023 18:24:41 -0500 Message-ID: <20231107232446.3776662-5-sashal@kernel.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231107232446.3776662-1-sashal@kernel.org> References: <20231107232446.3776662-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 5.15.137 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Marco Elver [ Upstream commit 355f074609dbf3042900ea9d30fcd2b0c323a365 ] syzbot reported: | BUG: KCSAN: data-race in p9_fd_create / p9_fd_create | | read-write to 0xffff888130fb3d48 of 4 bytes by task 15599 on cpu 0: | p9_fd_open net/9p/trans_fd.c:842 [inline] | p9_fd_create+0x210/0x250 net/9p/trans_fd.c:1092 | p9_client_create+0x595/0xa70 net/9p/client.c:1010 | v9fs_session_init+0xf9/0xd90 fs/9p/v9fs.c:410 | v9fs_mount+0x69/0x630 fs/9p/vfs_super.c:123 | legacy_get_tree+0x74/0xd0 fs/fs_context.c:611 | vfs_get_tree+0x51/0x190 fs/super.c:1519 | do_new_mount+0x203/0x660 fs/namespace.c:3335 | path_mount+0x496/0xb30 fs/namespace.c:3662 | do_mount fs/namespace.c:3675 [inline] | __do_sys_mount fs/namespace.c:3884 [inline] | [...] | | read-write to 0xffff888130fb3d48 of 4 bytes by task 15563 on cpu 1: | p9_fd_open net/9p/trans_fd.c:842 [inline] | p9_fd_create+0x210/0x250 net/9p/trans_fd.c:1092 | p9_client_create+0x595/0xa70 net/9p/client.c:1010 | v9fs_session_init+0xf9/0xd90 fs/9p/v9fs.c:410 | v9fs_mount+0x69/0x630 fs/9p/vfs_super.c:123 | legacy_get_tree+0x74/0xd0 fs/fs_context.c:611 | vfs_get_tree+0x51/0x190 fs/super.c:1519 | do_new_mount+0x203/0x660 fs/namespace.c:3335 | path_mount+0x496/0xb30 fs/namespace.c:3662 | do_mount fs/namespace.c:3675 [inline] | __do_sys_mount fs/namespace.c:3884 [inline] | [...] | | value changed: 0x00008002 -> 0x00008802 Within p9_fd_open(), O_NONBLOCK is added to f_flags of the read and write files. This may happen concurrently if e.g. mounting process modifies the fd in another thread. Mark the plain read-modify-writes as intentional data-races, with the assumption that the result of executing the accesses concurrently will always result in the same result despite the accesses themselves not being atomic. Reported-by: syzbot+e441aeeb422763cc5511@syzkaller.appspotmail.com Signed-off-by: Marco Elver Link: https://lore.kernel.org/r/ZO38mqkS0TYUlpFp@elver.google.com Signed-off-by: Dominique Martinet Message-ID: <20231025103445.1248103-1-asmadeus@codewreck.org> Signed-off-by: Sasha Levin --- net/9p/trans_fd.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c index f359cfdc1858f..b44b77d3b35d1 100644 --- a/net/9p/trans_fd.c +++ b/net/9p/trans_fd.c @@ -835,14 +835,21 @@ static int p9_fd_open(struct p9_client *client, int rfd, int wfd) goto out_free_ts; if (!(ts->rd->f_mode & FMODE_READ)) goto out_put_rd; - /* prevent workers from hanging on IO when fd is a pipe */ - ts->rd->f_flags |= O_NONBLOCK; + /* Prevent workers from hanging on IO when fd is a pipe. + * It's technically possible for userspace or concurrent mounts to + * modify this flag concurrently, which will likely result in a + * broken filesystem. However, just having bad flags here should + * not crash the kernel or cause any other sort of bug, so mark this + * particular data race as intentional so that tooling (like KCSAN) + * can allow it and detect further problems. + */ + data_race(ts->rd->f_flags |= O_NONBLOCK); ts->wr = fget(wfd); if (!ts->wr) goto out_put_rd; if (!(ts->wr->f_mode & FMODE_WRITE)) goto out_put_wr; - ts->wr->f_flags |= O_NONBLOCK; + data_race(ts->wr->f_flags |= O_NONBLOCK); client->trans = ts; client->status = Connected; -- 2.42.0