From b409946b2a3c1ddcde75e5f35a77e03f4d354be0 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Tue, 25 Apr 2017 20:49:24 +1000 Subject: powerpc/mm: Fix possible out-of-bounds shift in arch_mmap_rnd() The recent patch to add runtime configuration of the ASLR limits added a bug in arch_mmap_rnd() where we may shift an integer (32-bits) by up to 33 bits, leading to undefined behaviour. In practice it exhibits as every process seg faulting instantly, presumably because the rnd value hasn't been restricited by the modulus at all. We didn't notice because it only happens under certain kernel configurations and if the number of bits is actually set to a large value. Fix it by switching to unsigned long. Fixes: 9fea59bd7ca5 ("powerpc/mm: Add support for runtime configuration of ASLR limits") Reported-by: Balbir Singh Reviewed-by: Kees Cook Signed-off-by: Michael Ellerman --- arch/powerpc/mm/mmap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/powerpc') diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c index 005aa8a44915..9dbd2a733d6b 100644 --- a/arch/powerpc/mm/mmap.c +++ b/arch/powerpc/mm/mmap.c @@ -66,7 +66,7 @@ unsigned long arch_mmap_rnd(void) if (is_32bit_task()) shift = mmap_rnd_compat_bits; #endif - rnd = get_random_long() % (1 << shift); + rnd = get_random_long() % (1ul << shift); return rnd << PAGE_SHIFT; } -- cgit v1.2.3