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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). Signed-off-by: Julien Tinnes <jt@cr0.org> Signed-off-by: Tavis Ormandy <taviso@sdf.lonestar.org> Cc: stable@kernel.org Acked-by: Christoph Hellwig <hch@infradead.org> Acked-by: Kees Cook <kees@ubuntu.com> Acked-by: Eugene Teo <eugene@redhat.com> [ Shortened lines and fixed whitespace as per Christophs' suggestion ] Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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