From f9fabcb58a6d26d6efde842d1703ac7cfa9427b6 Mon Sep 17 00:00:00 2001 From: Julien Tinnes Date: Fri, 26 Jun 2009 20:27:40 +0200 Subject: [PATCH] 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 Signed-off-by: Tavis Ormandy Cc: stable@kernel.org Acked-by: Christoph Hellwig Acked-by: Kees Cook Acked-by: Eugene Teo [ Shortened lines and fixed whitespace as per Christophs' suggestion ] Signed-off-by: Linus Torvalds --- include/linux/personality.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/include/linux/personality.h b/include/linux/personality.h index a84e9ff9b27..126120819a0 100644 --- 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. -- 2.20.1