Date: Thu, 16 Jul 2009 10:30:42 +0200 From: Marcus Meissner <meissner@...e.de> To: oss-security@...ts.openwall.com Cc: "Steven M. Christey" <coley@...us.mitre.org> Subject: Re: CVE-2009-1895 kernel: personality: fix PER_CLEAR_ON_SETID On Thu, Jul 16, 2009 at 02:49:02PM +0800, Eugene Teo wrote: > Reported by Julien Tinnes. > > "We have found that the current PER_CLEAR_ON_SETID mask on Linux doesn't > include neither ADDR_COMPAT_LAYOUT, nor MMAP_PAGE_ZERO. > > The current mask is READ_IMPLIES_EXEC|ADDR_NO_RANDOMIZE. > > We believe it is important to add MMAP_PAGE_ZERO, because by using this > personality it is possible to have the first page mapped inside a > process running as setuid root. This could be used in those scenarios: > > - Exploiting a NULL pointer dereference issue in a setuid root binary > - Bypassing the mmap_min_addr restrictions of the Linux kernel: by > running a setuid binary that would drop privileges before giving us > control back (for instance by loading a user-supplied library), we could > get the first page mapped in a process we control. By further using > mremap and mprotect on this mapping, we can then completely bypass the > mmap_min_addr restrictions. > > Less importantly, we believe ADDR_COMPAT_LAYOUT should also be added > since on x86 32bits it will in practice disable most of the address > space layout randomization (only the stack will remain randomized)." > > Upstream commit: > http://git.kernel.org/linus/f9fabcb58a6d26d6efde842d1703ac7cfa9427b6 > > References: > https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2009-1895 > http://blog.cr0.org/2009/06/bypassing-linux-null-pointer.html > http://patchwork.kernel.org/patch/32598/ > http://marc.info/?l=linux-security-module&m=124724852000951&w=2 Also http://www.securityfocus.com/bid/35647 Ciao, Marcus
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