[patch 04/24] personality: fix PER_CLEAR_ON_SETID (CVE-2009-1895)

Greg KH
2009-07-17T20:23:57Z

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2.6.30-stable review patch. If anyone has any objections, please let us know.

------------------

From: Julien Tinnes <jt@cr0.org>

commit f9fabcb58a6d26d6efde842d1703ac7cfa9427b6 upstream.

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>
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
include/linux/personality.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/include/linux/personality.h
+++ b/include/linux/personality.h
@@ -40,7 +40,10 @@ 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.