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| author | Roman Gushchin <klamm@yandex-team.ru> | 2015-02-11 15:28:39 -0800 |
|---|---|---|
| committer | Zefan Li <lizefan@huawei.com> | 2015-06-19 11:40:15 +0800 |
| commit | dcdcb2bd6bc0e49f1d38f25b729bf51ea743569d (patch) | |
| tree | d3119fd2663307abed1cfdd9d43def199ee376f1 | |
| parent | 2a4edc62b38380cd464fc4b65524f626bf76fb1f (diff) | |
| download | lwn-dcdcb2bd6bc0e49f1d38f25b729bf51ea743569d.tar.gz lwn-dcdcb2bd6bc0e49f1d38f25b729bf51ea743569d.zip | |
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 <klamm@yandex-team.ru>
Cc: Andrew Shewmaker <agshew@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
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>
| -rw-r--r-- | mm/mmap.c | 2 |
1 files changed, 1 insertions, 1 deletions
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); |