From 0fbb5b27ebef70a079447988ed38e657e7f17256 Mon Sep 17 00:00:00 2001 From: Roman Gushchin Date: Wed, 11 Feb 2015 15:28:42 -0800 Subject: [PATCH] mm/nommu.c: fix arithmetic overflow in __vm_enough_memory() commit 8138a67a5557ffea3a21dfd6f037842d4e748513 upstream. 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. Signed-off-by: Roman Gushchin Cc: Andrew Shewmaker Cc: Rik van Riel Cc: Konstantin Khlebnikov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: there is no 'reserved' variable] Signed-off-by: Ben Hutchings --- mm/nommu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/nommu.c b/mm/nommu.c index 1db797136f48..d0cb11fbe679 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1885,7 +1885,7 @@ EXPORT_SYMBOL(unmap_mapping_range); */ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin) { - unsigned long free, allowed; + long free, allowed; vm_acct_memory(pages); -- 2.39.2