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From: Roman Gushchin <klamm@yandex-team.ru>
To: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org,
Roman Gushchin <klamm@yandex-team.ru>,
Andrew Morton <akpm@linux-foundation.org>,
Andrew Shewmaker <agshew@gmail.com>,
Rik van Riel <riel@redhat.com>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
stable@vger.kernel.org
Subject: [PATCH] mm: fix arithmetic overflow in __vm_enough_memory()
Date: Thu, 29 Jan 2015 16:06:03 +0300 [thread overview]
Message-ID: <1422536763-31325-1-git-send-email-klamm@yandex-team.ru> (raw)
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 <klamm@yandex-team.ru>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrew Shewmaker <agshew@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: stable@vger.kernel.org
---
mm/mmap.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 7f684d5..5aa8dfe 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -152,7 +152,7 @@ EXPORT_SYMBOL_GPL(vm_memory_committed);
*/
int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
{
- unsigned long free, allowed, reserve;
+ long free, allowed, reserve;
VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) <
-(s64)vm_committed_as_batch * num_online_cpus(),
@@ -220,7 +220,7 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
*/
if (mm) {
reserve = sysctl_user_reserve_kbytes >> (PAGE_SHIFT - 10);
- allowed -= min(mm->total_vm / 32, reserve);
+ allowed -= min((long)mm->total_vm / 32, reserve);
}
if (percpu_counter_read_positive(&vm_committed_as) < allowed)
--
2.1.0
next reply other threads:[~2015-01-29 13:14 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-29 13:06 Roman Gushchin [this message]
2015-01-29 19:57 ` Andrew Shewmaker
2015-01-30 13:09 ` [PATCH] mm/nommu.c: " Roman Gushchin
2015-01-30 13:14 ` [PATCH] mm: " Roman Gushchin
2015-02-03 13:29 ` Michal Hocko
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