Date: Wed, 28 Aug 2013 15:23:30 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: freebsd-emulation@FreeBSD.org Cc: freebsd-hackers@FreeBSD.org, freebsd-standards@FreeBSD.org, freebsd-security@FreeBSD.org Subject: Re: [kde-freebsd] virtualbox file dialog problem Message-ID: <521DEBC2.1080602@FreeBSD.org> In-Reply-To: <521DE891.9070107@FreeBSD.org> References: <51E6B030.1080009@FreeBSD.org> <alpine.BSF.2.00.1307171910260.2397@badger.tharned.org> <51E793DB.2020607@FreeBSD.org> <521DE891.9070107@FreeBSD.org>
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on 28/08/2013 15:09 Andriy Gapon said the following: > Now a description of the problem. > > 1. VirtualBox executable is installed setuid root. Apparently, when it is run > it does some privileged things and then drops all of the uids and gids (real, > effective and saved) back to what they should have been originally. > VirtualBox does not do any (re-)exec of itself after the above manipulations. > > 2. issetugid(2) (which is apparently a BSD extension) on FreeBSD does not > consider the above manipulations as sufficient to mark an executable as > untainted. So it would return 1 for the VirtualBox process. > > 3. dbus code seems to impose some limitations on communication by such "tainted" > processes. It has the following code: > http://cgit.freedesktop.org/dbus/dbus/tree/dbus/dbus-sysdeps-unix.c#n4139 > For web-impaired :) the gist is that on BSD systems the code uses issetugid but > on other systems (like Linux) it uses getresuid and getresgid and checks that > all 3 uids are the same and all 3 gids are the same. > > As a result, on FreeBSD the dbus code would consider the VirtualBox process > tainted and that impairs its communication with KDE components. > On systems without issetugid or those that implement it differently, dbus would > work as for a normal process and all the communications are OK. > > I've also verified this conclusion by forcing dbus to use the alternative logic > on FreeBSD. > > So, possible solutions: [snip] > B. change VirtualBox to be friendly to FreeBSD issetugid(2) and exec itself > after dropping the privileges [snip] BTW, I've just found this "interesting" code in the VirtualBox sources (forgive me a full paste, but I couldn't resist): #if defined(RT_OS_DARWIN) # include <dlfcn.h> # include <sys/mman.h> # include <iprt/asm.h> # include <iprt/system.h> /** Really ugly hack to shut up a silly check in AppKit. */ static void ShutUpAppKit(void) { /* Check for Snow Leopard or higher */ char szInfo[64]; int rc = RTSystemQueryOSInfo (RTSYSOSINFO_RELEASE, szInfo, sizeof(szInfo)); if ( RT_SUCCESS (rc) && szInfo[0] == '1') /* higher than 1x.x.x */ { /* * Find issetguid() and make it always return 0 by modifying the code. */ void *addr = dlsym(RTLD_DEFAULT, "issetugid"); int rc = mprotect((void *)((uintptr_t)addr & ~(uintptr_t)0xfff), 0x2000, PROT_WRITE|PROT_READ|PROT_EXEC); if (!rc) ASMAtomicWriteU32((volatile uint32_t *)addr, 0xccc3c031); /* xor eax, eax; ret; int3 */ } } #endif /* DARWIN */ -- Andriy Gapon
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