From nobody Fri Nov 22 15:56:54 2024 Received: from forward101a.mail.yandex.net (forward101a.mail.yandex.net [178.154.239.84]) (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 405D228FF; Sat, 16 Nov 2024 20:23:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=178.154.239.84 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731788618; cv=none; b=t+27V6cO2BL+Ztx/4uqHD8y41rFBQSnNi2cako2wL8aAn+4zZezja6TxBYbw9uPGVeczt2T0urSyPAtvRWPh2YcgdWpJCx+Q3jUqbQVWkv6jZUiBMxB1YUIcQiuZ6/8c3T0/PIIjP6hDU10B9ydnsDMtoAfzHPj6HFpSWZMAsMg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731788618; c=relaxed/simple; bh=Xwt1wgD3GpJFJvVO6W3Kf69DFMrYWLJzBt+Q+zwdm+0=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=GcloqygU2PFy9vQHKKPlVtEIx40TQr974h5neSMAniztWwMjDrrxdy6/T5FBhqTydF9HNJDKjGkt3L3766Igur+l8Rzym8mXLwObfIA7wi4OteZ/gW0Uw7Zi3yGyQ3WSqt1atlrPIiWeyH5TF7lAUtZKgTWAds2zHtecV5rJqPw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=yandex.ru; spf=pass smtp.mailfrom=yandex.ru; dkim=pass (1024-bit key) header.d=yandex.ru header.i=@yandex.ru header.b=lmoYsacE; arc=none smtp.client-ip=178.154.239.84 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=yandex.ru Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=yandex.ru Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=yandex.ru header.i=@yandex.ru header.b="lmoYsacE" Received: from mail-nwsmtp-smtp-production-main-68.vla.yp-c.yandex.net (mail-nwsmtp-smtp-production-main-68.vla.yp-c.yandex.net [IPv6:2a02:6b8:c1d:3e83:0:640:307a:0]) by forward101a.mail.yandex.net (Yandex) with ESMTPS id E5A9860039; Sat, 16 Nov 2024 23:23:24 +0300 (MSK) Received: by mail-nwsmtp-smtp-production-main-68.vla.yp-c.yandex.net (smtp/Yandex) with ESMTPSA id LNVPeYOOouQ0-0ivAiGht; Sat, 16 Nov 2024 23:23:23 +0300 X-Yandex-Fwd: 1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex.ru; s=mail; t=1731788603; bh=O31CYpoIo+My2OpOnR9CiaJUHu/xs78IoYQDtcJ0LqQ=; h=Message-ID:Date:Cc:Subject:To:From; b=lmoYsacE+Sy+VMXQJRteDwFsxIILrj5k8mhabMMexsWuSGk5t3RvuTQaG+FGVmCf5 t6iDNm4u2wRuUHbTCJ/7i2o0Tbe+evaMcaIztP7pnLFFjzH37D93PRfW+nn11MacSG FTZSdAUWuIqj35xxvfQwNcfkI6oRSABIH/ljeY7A= Authentication-Results: mail-nwsmtp-smtp-production-main-68.vla.yp-c.yandex.net; dkim=pass header.i=@yandex.ru From: Stas Sergeev To: linux-kernel@vger.kernel.org Cc: Stas Sergeev , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Christian Brauner , Kees Cook , Kuniyuki Iwashima , netdev@vger.kernel.org Subject: [PATCH net] scm: fix negative fds with SO_PASSPIDFD Date: Sat, 16 Nov 2024 23:23:05 +0300 Message-ID: <20241116202306.937322-1-stsp2@yandex.ru> X-Mailer: git-send-email 2.47.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" pidfd_prepare() can return negative values as an error codes. But scm_pidfd_recv() didn't check for that condition. As the result, it is possible to create the race that leads to the negative fds. The race happens if the peer process sends something to SO_PASSPIDFD-enabled recipient, and quickly exits. pidfd_prepare() has this code: if (!pid || !pid_has_task(pid, thread ? PIDTYPE_PID : PIDTYPE_TGID)) return -EINVAL; So if you exit quickly enough, you can hit that EINVAL. Getting the fd=3D-22 is very weird, if not exploitable. This patch adds the missing check and sets MSG_CTRUNC on error. Recipient can now detect an error by checking this flag. Signed-off-by: Stas Sergeev CC: "David S. Miller" CC: Eric Dumazet CC: Jakub Kicinski CC: Paolo Abeni CC: Simon Horman CC: Christian Brauner CC: Kees Cook CC: Kuniyuki Iwashima CC: netdev@vger.kernel.org CC: linux-kernel@vger.kernel.org --- include/net/scm.h | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/include/net/scm.h b/include/net/scm.h index 0d35c7c77a74..3ccf8546c506 100644 --- a/include/net/scm.h +++ b/include/net/scm.h @@ -155,6 +155,10 @@ static __inline__ void scm_pidfd_recv(struct msghdr *m= sg, struct scm_cookie *scm return; =20 pidfd =3D pidfd_prepare(scm->pid, 0, &pidfd_file); + if (pidfd < 0) { + msg->msg_flags |=3D MSG_CTRUNC; + return; + } =20 if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) { if (pidfd_file) { --=20 2.47.0