Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754635AbbEECR0 (ORCPT ); Mon, 4 May 2015 22:17:26 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:50865 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752053AbbEEBV5 (ORCPT ); Mon, 4 May 2015 21:21:57 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Jann Horn" , "Linus Torvalds" Date: Tue, 05 May 2015 02:16:39 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 180/221] fs: take i_mutex during prepare_binprm for set[ug]id executables In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3160 Lines: 115 3.2.69-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Jann Horn commit 8b01fc86b9f425899f8a3a8fc1c47d73c2c20543 upstream. This prevents a race between chown() and execve(), where chowning a setuid-user binary to root would momentarily make the binary setuid root. This patch was mostly written by Linus Torvalds. Signed-off-by: Jann Horn Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: - Drop the task_no_new_privs() and user namespace checks - Open-code file_inode() - s/READ_ONCE/ACCESS_ONCE/ - Adjust context] Signed-off-by: Ben Hutchings --- --- a/fs/exec.c +++ b/fs/exec.c @@ -1282,6 +1282,45 @@ int check_unsafe_exec(struct linux_binpr return res; } +static void bprm_fill_uid(struct linux_binprm *bprm) +{ + struct inode *inode; + unsigned int mode; + uid_t uid; + gid_t gid; + + /* clear any previous set[ug]id data from a previous binary */ + bprm->cred->euid = current_euid(); + bprm->cred->egid = current_egid(); + + if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) + return; + + inode = bprm->file->f_path.dentry->d_inode; + mode = ACCESS_ONCE(inode->i_mode); + if (!(mode & (S_ISUID|S_ISGID))) + return; + + /* Be careful if suid/sgid is set */ + mutex_lock(&inode->i_mutex); + + /* reload atomically mode/uid/gid now that lock held */ + mode = inode->i_mode; + uid = inode->i_uid; + gid = inode->i_gid; + mutex_unlock(&inode->i_mutex); + + if (mode & S_ISUID) { + bprm->per_clear |= PER_CLEAR_ON_SETID; + bprm->cred->euid = uid; + } + + if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { + bprm->per_clear |= PER_CLEAR_ON_SETID; + bprm->cred->egid = gid; + } +} + /* * Fill the binprm structure from the inode. * Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes @@ -1290,36 +1329,12 @@ int check_unsafe_exec(struct linux_binpr */ int prepare_binprm(struct linux_binprm *bprm) { - umode_t mode; - struct inode * inode = bprm->file->f_path.dentry->d_inode; int retval; - mode = inode->i_mode; if (bprm->file->f_op == NULL) return -EACCES; - /* clear any previous set[ug]id data from a previous binary */ - bprm->cred->euid = current_euid(); - bprm->cred->egid = current_egid(); - - if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)) { - /* Set-uid? */ - if (mode & S_ISUID) { - bprm->per_clear |= PER_CLEAR_ON_SETID; - bprm->cred->euid = inode->i_uid; - } - - /* Set-gid? */ - /* - * If setgid is set but no group execute bit then this - * is a candidate for mandatory locking, not a setgid - * executable. - */ - if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { - bprm->per_clear |= PER_CLEAR_ON_SETID; - bprm->cred->egid = inode->i_gid; - } - } + bprm_fill_uid(bprm); /* fill in binprm security blob */ retval = security_bprm_set_creds(bprm); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/