From dcdcb2bd6bc0e49f1d38f25b729bf51ea743569d 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() commit 5703b087dc8eaf47bfb399d6cf512d471beff405 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. [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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [lizf: Backported to 3.4: - adjust context - there's no variable reserve] Signed-off-by: Zefan Li --- mm/mmap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mmap.c b/mm/mmap.c index 208e70f1006d..cb6456d35860 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -112,7 +112,7 @@ struct percpu_counter vm_committed_as ____cacheline_aligned_in_smp; */ 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);