From a818777d4249e934ef7c9e6e7df8475d6692f315 Mon Sep 17 00:00:00 2001 From: Daniel Thompson Date: Tue, 12 May 2015 07:56:04 +0100 Subject: [PATCH] libbb: Enable support for !CONFIG_MULTIUSER 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 Signed-off-by: Denys Vlasenko --- libbb/change_identity.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/libbb/change_identity.c b/libbb/change_identity.c index 619db09a8..d48d86326 100644 --- a/libbb/change_identity.c +++ b/libbb/change_identity.c @@ -33,9 +33,28 @@ /* Become the user and group(s) specified by PW. */ void FAST_FUNC change_identity(const struct passwd *pw) { - if (initgroups(pw->pw_name, pw->pw_gid) == -1) - bb_perror_msg_and_die("can't set groups"); + int res; + + res = initgroups(pw->pw_name, pw->pw_gid); endgrent(); /* helps to close a fd used internally by libc */ + + if (res != 0) { + /* + * If initgroups() fails because a system call is unimplemented + * then we are running on a Linux kernel compiled without multiuser + * support (CONFIG_MULTIUSER is not defined). + * + * If we are running without multiuser support *and* the target uid + * already matches the current uid then we can skip the change of + * identity. + */ + if (errno == ENOSYS && pw->pw_uid == getuid()) { + return; + } + + bb_perror_msg_and_die("can't set groups"); + } + xsetgid(pw->pw_gid); xsetuid(pw->pw_uid); } -- 2.25.1