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personality: fix PER_CLEAR_ON_SETID

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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>
This commit is contained in:
Julien Tinnes 2009-06-26 20:27:40 +02:00 committed by Linus Torvalds
parent a137802ee8
commit f9fabcb58a
1 changed files with 4 additions and 1 deletions
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5
include/linux/personality.h
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@ -40,7 +40,10 @@ enum {
* Security-relevant compatibility flags that must be * Security-relevant compatibility flags that must be
* cleared upon setuid or setgid exec: * 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. * Personality types.