Date: Thu, 7 Jun 2007 17:35:39 -0400 From: Mike Meyer <mwm@mired.org> To: Stanislav Sedov <stas@FreeBSD.org> Cc: freebsd-hackers@FreeBSD.org, timur@gnu.org, freebsd-arch@FreeBSD.org Subject: Re: setegid bug Message-ID: <18024.31275.733694.236655@bhuda.mired.org> In-Reply-To: <20070607213650.c02130bf.stas@FreeBSD.org> References: <20070607213650.c02130bf.stas@FreeBSD.org>
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In <20070607213650.c02130bf.stas@FreeBSD.org>, Stanislav Sedov <stas@FreeBSD.org> typed: > Recently several FreeBSD samba users reported a scary problem with > samba (http://bugzilla.samba.org/?id=3990). Further research in > cooperation with Timur Bakeyev (timur) showed, that we have a little > problem with setegid implementation. In FreeBSD (and even in > 4.4BSD-Lite2) egid of the process is merely groups[0], so calling > seteuid function we simply override the first of supplementary groups. > However, POSIX says that not rgid, not any of supplementary groups > should bot be rewritten in setegid call. > > Probably, some of old-school committers remembered the initial > intention of making egid equal to groups[0]? Probably, I have missed > something? The old school in this case is UC Berkeley. I found this behavior in 4.1BSD. Since it lets you violate ass-backwards group security settings (wherein you create a group "undesirables", and have files owned by that group with group bits 0 to keep them out) by removing yourself from that group, I reported it as a security bug to CSRG. Mike's response was that the security model was the bug, not this problem. I suspect it was done that way in the initial implementation, and nobody has ever felt that it should be fixed. <mike -- Mike Meyer <mwm@mired.org> http://www.mired.org/consulting.html Independent Network/Unix/Perforce consultant, email for more information.
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