From b3a633c8527ef155b1a4e22e8f5abc58f7af54c9 Mon Sep 17 00:00:00 2001 From: Julien Tinnes Date: Fri, 10 Jul 2009 10:46:30 -0700 Subject: [PATCH] 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 --- include/linux/personality.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/include/linux/personality.h b/include/linux/personality.h index a84e9ff9b27e..b7f578dac544 100644 --- a/include/linux/personality.h +++ b/include/linux/personality.h @@ -40,7 +40,11 @@ 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.