diff options
author | Roman Gushchin <klamm@yandex-team.ru> | 2015-02-11 15:28:42 -0800 |
---|---|---|
committer | Zefan Li <lizefan@huawei.com> | 2015-06-19 11:40:15 +0800 |
commit | edc438c180faa9053f94f9ea5149c2be20c5126c (patch) | |
tree | 23d2972d4b08dfaf7177c14b8eb87d9b3b2a071e /mm | |
parent | dcdcb2bd6bc0e49f1d38f25b729bf51ea743569d (diff) | |
download | lwn-edc438c180faa9053f94f9ea5149c2be20c5126c.tar.gz lwn-edc438c180faa9053f94f9ea5149c2be20c5126c.zip |
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 <klamm@yandex-team.ru>
Cc: Andrew Shewmaker <agshew@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[lizf: Backported to 3.4:
- adjust context
- there's no variable reserve]
Signed-off-by: Zefan Li <lizefan@huawei.com>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/nommu.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/nommu.c b/mm/nommu.c index d3afb4765c8a..3f282f9cc13f 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1916,7 +1916,7 @@ 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); |