Messages in this thread Patch in this message | | | Date | Fri, 26 Jun 2009 20:27:40 +0200 | Subject | [patch 1/1] personality handling: fix PER_CLEAR_ON_SETID for security reasons | From | Julien Tinnes <> |
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Hello,
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> and Tavis Ormandy <taviso@sdf.lonestar.org>
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diff -r f70f443c9ead include/linux/personality.h --- a/include/linux/personality.h Fri Jun 26 19:59:33 2009 +0200 +++ b/include/linux/personality.h Fri Jun 26 20:00:40 2009 +0200 @@ -40,7 +40,7 @@ enum { * Security-relevant compatibility flags that must be * cleared upon setuid or setgid exec: */ -#define PER_CLEAR_ON_SETID (READ_IMPLIES_EXEC|ADDR_NO_RANDOMIZE) +#define PER_CLEAR_ON_SETID (READ_IMPLIES_EXEC|ADDR_NO_RANDOMIZE|ADDR_COMPAT_LAYOUT|MMAP_PAGE_ZERO)
/* * Personality types.
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