Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752750AbdGRW0A (ORCPT ); Tue, 18 Jul 2017 18:26:00 -0400 Received: from mail-pg0-f52.google.com ([74.125.83.52]:36512 "EHLO mail-pg0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752642AbdGRWZt (ORCPT ); Tue, 18 Jul 2017 18:25:49 -0400 From: Kees Cook To: Andrew Morton Cc: Kees Cook , Serge Hallyn , Andy Lutomirski , David Howells , "Eric W. Biederman" , John Johansen , Paul Moore , Stephen Smalley , Casey Schaufler , Tetsuo Handa , James Morris , Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 06/15] commoncap: Refactor to remove bprm_secureexec hook Date: Tue, 18 Jul 2017 15:25:27 -0700 Message-Id: <1500416736-49829-7-git-send-email-keescook@chromium.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1500416736-49829-1-git-send-email-keescook@chromium.org> References: <1500416736-49829-1-git-send-email-keescook@chromium.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4562 Lines: 116 The commoncap implementation of the bprm_secureexec hook is the only LSM that depends on the final call to its bprm_set_creds hook (since it may be called for multiple files, it ignores bprm->called_set_creds). As a result, it cannot safely _clear_ bprm->secureexec since other LSMs may have set it. Instead, remove the bprm_secureexec hook by introducing a new flag to bprm specific to commoncap: cap_elevated. This is similar to cap_effective, but that is used for a specific subset of elevated privileges, and exists solely to track state from bprm_set_creds to bprm_secureexec. As such, it will be removed in the next patch. Here, set the new bprm->cap_elevated flag when setuid/setgid has happened from bprm_fill_uid() or fscapabilities have been prepared. This temporarily moves the bprm_secureexec hook to a static inline. The helper will be removed in the next patch; this makes the step easier to review and bisect, since this does not introduce any changes to inputs nor outputs to the "elevated privileges" calculation. The new flag is merged with the bprm->secureexec flag in setup_new_exec() since this marks the end of any further prepare_binprm() calls. Cc: Serge Hallyn Cc: Andy Lutomirski Signed-off-by: Kees Cook --- fs/exec.c | 7 +++++++ include/linux/binfmts.h | 7 +++++++ security/commoncap.c | 12 ++++++++---- 3 files changed, 22 insertions(+), 4 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 925c85a45d97..53ffa739fb58 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1330,6 +1330,13 @@ EXPORT_SYMBOL(would_dump); void setup_new_exec(struct linux_binprm * bprm) { + /* + * Once here, prepare_binrpm() will not be called any more, so + * the final state of setuid/setgid/fscaps can be merged into the + * secureexec flag. + */ + bprm->secureexec |= bprm->cap_elevated; + arch_pick_mmap_layout(current->mm); /* This is the point of no return */ diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index 36be5a67517a..a82f5edf23f9 100644 --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -35,6 +35,13 @@ struct linux_binprm { * false if not; except for init which inherits * its parent's caps anyway */ /* + * True if most recent call to the commoncaps bprm_set_creds + * hook (due to multiple prepare_binprm() calls from the + * binfmt_script/misc handlers) resulted in elevated + * privileges. + */ + cap_elevated:1, + /* * Set by bprm_set_creds hook to indicate a privilege-gaining * exec has happened. Used to sanitize execution environment * and to set AT_SECURE auxv for glibc. diff --git a/security/commoncap.c b/security/commoncap.c index 7abebd782d5e..abb6050c8083 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -481,6 +481,8 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c return rc; } +static int is_secureexec(struct linux_binprm *bprm); + /** * cap_bprm_set_creds - Set up the proposed credentials for execve(). * @bprm: The execution parameters, including the proposed creds @@ -614,11 +616,14 @@ int cap_bprm_set_creds(struct linux_binprm *bprm) if (WARN_ON(!cap_ambient_invariant_ok(new))) return -EPERM; + /* Check for privilege-elevated exec. */ + bprm->cap_elevated = is_secureexec(bprm); + return 0; } /** - * cap_bprm_secureexec - Determine whether a secure execution is required + * is_secureexec - Determine whether a secure execution is required * @bprm: The execution parameters * * Determine whether a secure execution is required, return 1 if it is, and 0 @@ -627,9 +632,9 @@ int cap_bprm_set_creds(struct linux_binprm *bprm) * The credentials have been committed by this point, and so are no longer * available through @bprm->cred. */ -int cap_bprm_secureexec(struct linux_binprm *bprm) +static int is_secureexec(struct linux_binprm *bprm) { - const struct cred *cred = current_cred(); + const struct cred *cred = bprm->cred; kuid_t root_uid = make_kuid(cred->user_ns, 0); if (!uid_eq(cred->uid, root_uid)) { @@ -1079,7 +1084,6 @@ struct security_hook_list capability_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(capget, cap_capget), LSM_HOOK_INIT(capset, cap_capset), LSM_HOOK_INIT(bprm_set_creds, cap_bprm_set_creds), - LSM_HOOK_INIT(bprm_secureexec, cap_bprm_secureexec), LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv), LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv), LSM_HOOK_INIT(mmap_addr, cap_mmap_addr), -- 2.7.4