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Linux recently gained a new config option, CONFIG_MULTIUSER, that makes support for non-root users optional. This results in a number of syscalls being disabled: setuid, setregid, setgid, setreuid, setresuid, getresuid, setresgid, getresgid, setgroups, getgroups, setfsuid, setfsgid, capget, capset. Currently a number of busybox applets, including login, struggle to run when CONFIG_MULTIUSER is disabled. Even the root user is unable to login: login: can't set groups: Functi This patch adds code to make change_identity() a nop on single user systems. It works by recognising the signature errno value (ENOSYS, due to the system calls being disabled) and, to avoid security risks, only deploys when the current uid and target uid is the same. After the patch is applied any attempt to switch to a non-root user will fail. Thus a badly configured userspace (for example, one that tries to start a daemon as a non-root user when the kernel cannot support this) will report errors as one would expect. Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
61 lines
2.3 KiB
C
61 lines
2.3 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* Copyright 1989 - 1991, Julianne Frances Haugh <jockgrrl@austin.rr.com>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of Julianne F. Haugh nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY JULIE HAUGH AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL JULIE HAUGH OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include "libbb.h"
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/* Become the user and group(s) specified by PW. */
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void FAST_FUNC change_identity(const struct passwd *pw)
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{
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int res;
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res = initgroups(pw->pw_name, pw->pw_gid);
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endgrent(); /* helps to close a fd used internally by libc */
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if (res != 0) {
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/*
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* If initgroups() fails because a system call is unimplemented
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* then we are running on a Linux kernel compiled without multiuser
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* support (CONFIG_MULTIUSER is not defined).
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*
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* If we are running without multiuser support *and* the target uid
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* already matches the current uid then we can skip the change of
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* identity.
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*/
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if (errno == ENOSYS && pw->pw_uid == getuid()) {
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return;
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}
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bb_perror_msg_and_die("can't set groups");
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}
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xsetgid(pw->pw_gid);
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xsetuid(pw->pw_uid);
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}
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