personality: fix PER_CLEAR_ON_SETID

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 <[email protected]>
Signed-off-by: Tavis Ormandy <[email protected]>
Cc: [email protected]
Acked-by: Christoph Hellwig <[email protected]>
Acked-by: Kees Cook <[email protected]>
Acked-by: Eugene Teo <[email protected]>
[ Shortened lines and fixed whitespace as per Christophs' suggestion ]
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions