From patchwork Mon Oct 23 23:37:02 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dominique Martinet X-Patchwork-Id: 13433717 Received: from nautica.notk.org (nautica.notk.org [91.121.71.147]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C0BDB2376A for ; Mon, 23 Oct 2023 23:37:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=codewreck.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=codewreck.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=codewreck.org header.i=@codewreck.org header.b="2DLrhRRq"; dkim=pass (2048-bit key) header.d=codewreck.org header.i=@codewreck.org header.b="H9q202+p" Received: by nautica.notk.org (Postfix, from userid 108) id 2CA8BC01F; Tue, 24 Oct 2023 01:37:23 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=codewreck.org; s=2; t=1698104243; bh=/A34CTskJseJi+dcqA1uEIZC2XG2pVw2hHNklQEakQo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2DLrhRRq6njg7SLrk3WbzcM8N/46q79mgTGyaP+Y4UsZA9IAsvLg8UrMUkQDnhLai 47r5jW+s0LYnQ+kUlpNRGbHdIW6ce4qjFqAWaNZGQb8wrYsLUmyBopuThwZQ4tzVLY ns++BcHak+wS9q+Mw+8M8i0lDqOVcr1rjCP1v236lW9x5gQ5pXmEqrhizKiIRIVnCf 1fT9nYAtamv3TQrZsgIRRhpgBjbiRhU+8KC+8nRYDmzXYaKdh3pWzZnbaT6IwiWe8a 28u3H1rA0xiZGPPfskQ8D76BQll/+zcjFRXNn8lP5TZktmJhEOLFMr+ojPRiiNtwgj iVL1rbm5tnGmw== X-Spam-Level: Received: from gaia (localhost [127.0.0.1]) by nautica.notk.org (Postfix) with ESMTPS id B3BC4C009; Tue, 24 Oct 2023 01:37:18 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=codewreck.org; s=2; t=1698104242; bh=/A34CTskJseJi+dcqA1uEIZC2XG2pVw2hHNklQEakQo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=H9q202+phVyt45nk/teha6weJN6/png6bkYoZNW6ao1p6BRyO4FgYWMGIk6gSm4yv x+Rdsf2lO5NyDeiJocV63AiF77nMyntK2AXb0yjd4QgRJaPRTcnGAizwfR8OFCU3Fh XGmc27IUykFBEgB2AYeA47YCFFx3H4+HUc2gTcEebovIS63OVAshRNGQGfhUF9UsAq VZKjILf2nDgY/sL0cr0KcwiBiGWQPEdquVObzzsD2EHShTwkze9tF78G9Qeztdu6lN OpODxoG+xIiGbgNx9U7Slo+cW1IeCiPRfOKXnae6VxgHyg2KvuSZJ1ZlcmsdakVcxP 7AD0G8iwggf8Q== Received: from gaia.codewreck.org (localhost.lan [::1]) by gaia (OpenSMTPD) with ESMTP id 1bf2bc7c; Mon, 23 Oct 2023 23:37:15 +0000 (UTC) From: Dominique Martinet To: v9fs@lists.linux.dev, ericvh@kernel.org, linux_oss@crudebyte.com Cc: lucho@ionkov.net, linux-kernel@vger.kernel.org, Marco Elver , syzbot+e441aeeb422763cc5511@syzkaller.appspotmail.com, Dominique Martinet Subject: [PATCH 1/3] 9p: Annotate data-racy writes to file::f_flags on fd mount Date: Tue, 24 Oct 2023 08:37:02 +0900 Message-ID: <20231023233704.1185154-2-asmadeus@codewreck.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20231023233704.1185154-1-asmadeus@codewreck.org> References: <20231023233704.1185154-1-asmadeus@codewreck.org> Precedence: bulk X-Mailing-List: v9fs@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Marco Elver 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 --- Hi Marco, sorry for taking ages to process this patch. I've reworded the commit message a bit and added a comment, so given this has your name on it please have a look. I'm planning to send this to Linus during the merge window next week net/9p/trans_fd.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c index f226953577b2..d89c88986950 100644 --- a/net/9p/trans_fd.c +++ b/net/9p/trans_fd.c @@ -836,14 +836,16 @@ 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 + * We don't support userspace messing with the fd after passing it + * to mount, so flag possible data race for KCSAN */ + 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;