path: root/security/Makefile
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authorJulien Tinnes <>2009-07-10 10:46:30 -0700
committerJames Morris <>2009-07-13 08:01:47 +1000
commitb3a633c8527ef155b1a4e22e8f5abc58f7af54c9 (patch)
tree4d5e16c82db298320c3515dca9f6eeca27164b3b /security/Makefile
parent8113a8d80f4c6a3dc3724b39b470f3fee9c426b6 (diff)
personality handling: fix PER_CLEAR_ON_SETID for security reasons
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 <> Signed-off-by: Tavis Ormandy <> Acked-by: Christoph Hellwig <> Acked-by: Kees Cook <> Signed-off-by: James Morris <>
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