From patchwork Wed Aug 21 09:56:05 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= X-Patchwork-Id: 13771161 X-Patchwork-Delegate: paul@paul-moore.com Received: from smtp-42a9.mail.infomaniak.ch (smtp-42a9.mail.infomaniak.ch [84.16.66.169]) (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 6DE711B2EC1 for ; Wed, 21 Aug 2024 09:56:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=84.16.66.169 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724234210; cv=none; b=r2hFgqYHtOl8aVgNrnsLf0hZzCe/kNLRyr8L/fg6Fy5DVaxwwk1pBee0uwrDjdWGyAHbI7aTTQD/3og6/SlOOEzYgZ8HskN5DigwAa+NnHoeGbQe0A15lhwML27Z1nOeuil0M4xStD/eGAsGVMppSlhNIGhqXjQoYPrCNoeN9LA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724234210; c=relaxed/simple; bh=HWH25yedLYdz8ph8RY73eXm+N0rL0t6KkJUIcf82vuM=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:Content-Type; b=Nj2A+MOrpVfun1c+Ojc/YFf9eCcIxGkfPnHdIPrI88tQ+YK8EmYZ1jRge7vOvUVnlvAJFsATeJzV4Be2vTrcp9sh8GkgIe0h59as/U0sC+naqu+xIu1bFHJTlCG4bhh1NcdkuCCt45nGK6P8k7M6dr0r9D5DHD2CWXEdsHyKonU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net; spf=pass smtp.mailfrom=digikod.net; dkim=pass (1024-bit key) header.d=digikod.net header.i=@digikod.net header.b=zDSvhaKH; arc=none smtp.client-ip=84.16.66.169 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=digikod.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=digikod.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=digikod.net header.i=@digikod.net header.b="zDSvhaKH" Received: from smtp-4-0000.mail.infomaniak.ch (smtp-4-0000.mail.infomaniak.ch [10.7.10.107]) by smtp-4-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4WphYl4rvFz19Jt; Wed, 21 Aug 2024 11:56:27 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digikod.net; s=20191114; t=1724234187; bh=yUyLTvLEaoLUHEgIZFvmpeRx32nYNt81EVAXTRpMemc=; h=From:To:Cc:Subject:Date:From; b=zDSvhaKHu+Wm4cRqIZyQdDaiV70hi7RZnioobuXfjPbQWQyiitSvNxM2OBuyrm8Uq jzw0avdMOz3+AQuLuQZEKyaFyUo0xT7FlRt1qTZOf2TldRDmzF9ik+HRLKHekELdOB CmfjJB4Q4y6FRPwOTmk7c541fWPTfFWuIaqWxgEM= Received: from unknown by smtp-4-0000.mail.infomaniak.ch (Postfix) with ESMTPA id 4WphYk49KczLLf; Wed, 21 Aug 2024 11:56:26 +0200 (CEST) From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: Christian Brauner , Paul Moore Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, Jan Kara , Tahera Fahimi , Mateusz Guzik , Al Viro , Casey Schaufler , James Morris , Jann Horn , Ondrej Mosnacek , "Serge E. Hallyn" , Stephen Smalley Subject: [PATCH v3 1/2] fs: Fix file_set_fowner LSM hook inconsistencies Date: Wed, 21 Aug 2024 11:56:05 +0200 Message-ID: <20240821095609.365176-1-mic@digikod.net> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Infomaniak-Routing: alpha The fcntl's F_SETOWN command sets the process that handle SIGIO/SIGURG for the related file descriptor. Before this change, the file_set_fowner LSM hook was always called, ignoring the VFS logic which may not actually change the process that handles SIGIO (e.g. TUN, TTY, dnotify), nor update the related UID/EUID. Moreover, because security_file_set_fowner() was called without lock (e.g. f_owner.lock), concurrent F_SETOWN commands could result to a race condition and inconsistent LSM states (e.g. SELinux's fown_sid) compared to struct fown_struct's UID/EUID. This change makes sure the LSM states are always in sync with the VFS state by moving the security_file_set_fowner() call close to the UID/EUID updates and using the same f_owner.lock . Rename f_modown() to __f_setown() to simplify code. Cc: Al Viro Cc: Casey Schaufler Cc: Christian Brauner Cc: James Morris Cc: Jann Horn Cc: Ondrej Mosnacek Cc: Paul Moore Cc: Serge E. Hallyn Cc: Stephen Smalley Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Mickaël Salaün --- Changes since v2: https://lore.kernel.org/r/20240812174421.1636724-1-mic@digikod.net - Only keep the LSM hook move. Changes since v1: https://lore.kernel.org/r/20240812144936.1616628-1-mic@digikod.net - Add back the file_set_fowner hook (but without user) as requested by Paul, but move it for consistency. --- fs/fcntl.c | 14 ++++---------- 1 file changed, 4 insertions(+), 10 deletions(-) diff --git a/fs/fcntl.c b/fs/fcntl.c index 300e5d9ad913..c28dc6c005f1 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -87,8 +87,8 @@ static int setfl(int fd, struct file * filp, unsigned int arg) return error; } -static void f_modown(struct file *filp, struct pid *pid, enum pid_type type, - int force) +void __f_setown(struct file *filp, struct pid *pid, enum pid_type type, + int force) { write_lock_irq(&filp->f_owner.lock); if (force || !filp->f_owner.pid) { @@ -98,19 +98,13 @@ static void f_modown(struct file *filp, struct pid *pid, enum pid_type type, if (pid) { const struct cred *cred = current_cred(); + security_file_set_fowner(filp); filp->f_owner.uid = cred->uid; filp->f_owner.euid = cred->euid; } } write_unlock_irq(&filp->f_owner.lock); } - -void __f_setown(struct file *filp, struct pid *pid, enum pid_type type, - int force) -{ - security_file_set_fowner(filp); - f_modown(filp, pid, type, force); -} EXPORT_SYMBOL(__f_setown); int f_setown(struct file *filp, int who, int force) @@ -146,7 +140,7 @@ EXPORT_SYMBOL(f_setown); void f_delown(struct file *filp) { - f_modown(filp, NULL, PIDTYPE_TGID, 1); + __f_setown(filp, NULL, PIDTYPE_TGID, 1); } pid_t f_getown(struct file *filp)