From 5703b087dc8eaf47bfb399d6cf512d471beff405 Mon Sep 17 00:00:00 2001 From: Roman Gushchin Date: Wed, 11 Feb 2015 15:28:39 -0800 Subject: [PATCH] mm/mmap.c: fix arithmetic overflow in __vm_enough_memory() I noticed, that "allowed" can easily overflow by falling below 0, because (total_vm / 32) can be larger than "allowed". The problem occurs in OVERCOMMIT_NONE mode. In this case, a huge allocation can success and overcommit the system (despite OVERCOMMIT_NONE mode). All subsequent allocations will fall (system-wide), so system become unusable. The problem was masked out by commit c9b1d0981fcc ("mm: limit growth of 3% hardcoded other user reserve"), but it's easy to reproduce it on older kernels: 1) set overcommit_memory sysctl to 2 2) mmap() large file multiple times (with VM_SHARED flag) 3) try to malloc() large amount of memory It also can be reproduced on newer kernels, but miss-configured sysctl_user_reserve_kbytes is required. Fix this issue by switching to signed arithmetic here. [akpm@linux-foundation.org: use min_t] Signed-off-by: Roman Gushchin Cc: Andrew Shewmaker Cc: Rik van Riel Cc: Konstantin Khlebnikov Reviewed-by: Michal Hocko Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-format-patch failed